Added Solution for 2021 day 24
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8
2021/day24_arithmetic_logic_unit/Cargo.toml
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8
2021/day24_arithmetic_logic_unit/Cargo.toml
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[package]
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name = "day24_arithmetic_logic_unit"
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version = "0.1.0"
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edition = "2021"
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# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
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[dependencies]
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84
2021/day24_arithmetic_logic_unit/challenge.txt
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84
2021/day24_arithmetic_logic_unit/challenge.txt
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[Magic smoke](https://en.wikipedia.org/wiki/Magic_smoke) starts leaking from the submarine's [arithmetic logic unit](https://en.wikipedia.org/wiki/Arithmetic_logic_unit) (ALU). Without the ability to perform basic arithmetic and logic functions, the submarine can't produce cool patterns with its Christmas lights!
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It also can't navigate. Or run the oxygen system.
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Don't worry, though - you *probably* have enough oxygen left to give you enough time to build a new ALU.
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The ALU is a four-dimensional processing unit: it has integer variables `w`, `x`, `y`, and `z`. These variables all start with the value `0`. The ALU also supports *six instructions*:
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* `inp a` - Read an input value and write it to variable `a`.
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* `add a b` - Add the value of `a` to the value of `b`, then store the result in variable `a`.
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* `mul a b` - Multiply the value of `a` by the value of `b`, then store the result in variable `a`.
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* `div a b` - Divide the value of `a` by the value of `b`, truncate the result to an integer, then store the result in variable `a`. (Here, "truncate" means to round the value toward zero.)
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* `mod a b` - Divide the value of `a` by the value of `b`, then store the *remainder* in variable `a`. (This is also called the [modulo](https://en.wikipedia.org/wiki/Modulo_operation) operation.)
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* `eql a b` - If the value of `a` and `b` are equal, then store the value `1` in variable `a`. Otherwise, store the value `0` in variable `a`.
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In all of these instructions, `a` and `b` are placeholders; `a` will always be the variable where the result of the operation is stored (one of `w`, `x`, `y`, or `z`), while `b` can be either a variable or a number. Numbers can be positive or negative, but will always be integers.
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The ALU has no *jump* instructions; in an ALU program, every instruction is run exactly once in order from top to bottom. The program halts after the last instruction has finished executing.
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(Program authors should be especially cautious; attempting to execute `div` with `b=0` or attempting to execute `mod` with `a<0` or `b<=0` will cause the program to crash and might even damage the ALU. These operations are never intended in any serious ALU program.)
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For example, here is an ALU program which takes an input number, negates it, and stores it in `x`:
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```
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inp x
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mul x -1
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```
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Here is an ALU program which takes two input numbers, then sets `z` to `1` if the second input number is three times larger than the first input number, or sets `z` to `0` otherwise:
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```
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inp z
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inp x
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mul z 3
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eql z x
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```
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Here is an ALU program which takes a non-negative integer as input, converts it into binary, and stores the lowest (1's) bit in `z`, the second-lowest (2's) bit in `y`, the third-lowest (4's) bit in `x`, and the fourth-lowest (8's) bit in `w`:
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```
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inp w
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add z w
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mod z 2
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div w 2
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add y w
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mod y 2
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div w 2
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add x w
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mod x 2
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div w 2
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mod w 2
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```
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Once you have built a replacement ALU, you can install it in the submarine, which will immediately resume what it was doing when the ALU failed: validating the submarine's *model number*. To do this, the ALU will run the MOdel Number Automatic Detector program (MONAD, your puzzle input).
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Submarine model numbers are always *fourteen-digit numbers* consisting only of digits `1` through `9`. The digit `0` *cannot* appear in a model number.
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When MONAD checks a hypothetical fourteen-digit model number, it uses fourteen separate `inp` instructions, each expecting a *single digit* of the model number in order of most to least significant. (So, to check the model number `13579246899999`, you would give `1` to the first `inp` instruction, `3` to the second `inp` instruction, `5` to the third `inp` instruction, and so on.) This means that when operating MONAD, each input instruction should only ever be given an integer value of at least `1` and at most `9`.
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Then, after MONAD has finished running all of its instructions, it will indicate that the model number was *valid* by leaving a `0` in variable `z`. However, if the model number was *invalid*, it will leave some other non-zero value in `z`.
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MONAD imposes additional, mysterious restrictions on model numbers, and legend says the last copy of the MONAD documentation was eaten by a [tanuki](https://en.wikipedia.org/wiki/Japanese_raccoon_dog). You'll need to *figure out what MONAD does* some other way.
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To enable as many submarine features as possible, find the largest valid fourteen-digit model number that contains no `0` digits. *What is the largest model number accepted by MONAD?*
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Your puzzle answer was `29991993698469`.
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\--- Part Two ---
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----------
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As the submarine starts booting up things like the [Retro Encabulator](https://www.youtube.com/watch?v=RXJKdh1KZ0w), you realize that maybe you don't need all these submarine features after all.
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*What is the smallest model number accepted by MONAD?*
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Your puzzle answer was `14691271141118`.
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Both parts of this puzzle are complete! They provide two gold stars: \*\*
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At this point, you should [return to your Advent calendar](/2021) and try another puzzle.
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If you still want to see it, you can [get your puzzle input](24/input).
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130
2021/day24_arithmetic_logic_unit/src/lib.rs
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130
2021/day24_arithmetic_logic_unit/src/lib.rs
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pub fn run() -> (usize, usize) {
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let first = next_valid_input(1_000_000, false);
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let second = next_valid_input(111_110, true);
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(first, second)
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}
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fn next_valid_input(previous: usize, ascending: bool) -> usize {
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let mut curr = if ascending {
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previous+1
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} else {
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previous-1
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};
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let mut digits: Vec<isize>;
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loop {
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digits = Vec::new();
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let mut rest = curr;
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while rest > 0 {
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let digit = rest % 10;
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if digit == 0 {
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if ascending {
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curr += 10_usize.pow(digits.len() as u32);
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} else {
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curr -= 10_usize.pow(digits.len() as u32);
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}
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digits = Vec::new();
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rest = curr;
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} else {
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digits.push(digit as isize);
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rest /= 10;
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}
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}
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// [0]=[13]-7
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// [1]=[12]+3
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// [2]=[11]+5
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// [3]=9
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// [4]=1
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// [5]=[10]+1
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// [6]=[7]+6
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// [8]=[9]-3
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//
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// free: 13, 12, 11, 10, 9, 7
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// [13] = 0
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// [12] = 1
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// [11] = 2
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// [10] = 3
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// [9] = 4
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// [8] = 5
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// [7] = 6
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let seven = digits.pop().unwrap();
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let next = digits[4] - 3;
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if (1..10).contains(&next) {
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digits.push(next);
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} else {
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if ascending {
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curr += 1;
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} else {
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curr -= 1;
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}
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continue;
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}
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digits.push(seven);
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let next = digits[6] + 6;
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if (1..10).contains(&next) {
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digits.push(next);
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} else {
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if ascending {
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curr += 1;
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} else {
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curr -= 1;
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}
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continue;
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}
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let next = digits[3] + 1;
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if (1..10).contains(&next) {
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digits.push(next);
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} else {
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if ascending {
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curr += 1;
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} else {
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curr -= 1;
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}
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continue;
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}
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digits.push(1);
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digits.push(9);
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let next = digits[2] + 5;
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if (1..10).contains(&next) {
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digits.push(next);
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} else {
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if ascending {
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curr += 1;
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} else {
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curr -= 1;
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}
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continue;
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}
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let next = digits[1] + 3;
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if (1..10).contains(&next) {
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digits.push(next);
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} else {
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if ascending {
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curr += 1;
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} else {
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curr -= 1;
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}
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continue;
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}
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let next = digits[0] - 7;
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if (1..10).contains(&next) {
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digits.push(next);
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break;
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} else if ascending {
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curr += 1;
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} else {
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curr -= 1;
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}
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}
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digits.iter().rev().fold(0, |acc, cur| 10*acc+ *cur as usize)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_challenge() {
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assert_eq!(run(), (29991993698469, 14691271141118));
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}
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}
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252
2021/day24_arithmetic_logic_unit/tests/challenge_input
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252
2021/day24_arithmetic_logic_unit/tests/challenge_input
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 15
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 9
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 11
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 1
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 10
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 11
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 12
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 3
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -11
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 10
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 11
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 5
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 14
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 0
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -6
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 7
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 1
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add x 10
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 9
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -6
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 15
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -6
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 4
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -16
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 10
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -4
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 4
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mul y x
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add z y
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inp w
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mul x 0
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add x z
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mod x 26
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div z 26
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add x -2
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eql x w
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eql x 0
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mul y 0
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add y 25
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mul y x
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add y 1
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mul z y
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mul y 0
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add y w
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add y 9
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mul y x
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add z y
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