Solutions for 2022, as well as 2015-2018 and 2019 up to day 11

2015/day04-ideal_stocking_suffer/Cargo.toml

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+[package]
+name = "day04-ideal_stocking_suffer"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+md-5 = "0.10.5"

2015/day04-ideal_stocking_suffer/challenge.txt

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+\--- Day 4: The Ideal Stocking Stuffer ---
+----------
+
+Santa needs help [mining](https://en.wikipedia.org/wiki/Bitcoin#Mining) some AdventCoins (very similar to [bitcoins](https://en.wikipedia.org/wiki/Bitcoin)) to use as gifts for all the economically forward-thinking little girls and boys.
+
+To do this, he needs to find [MD5](https://en.wikipedia.org/wiki/MD5) hashes which, in [hexadecimal](https://en.wikipedia.org/wiki/Hexadecimal), start with at least *five zeroes*. The input to the MD5 hash is some secret key (your puzzle input, given below) followed by a number in decimal. To mine AdventCoins, you must find Santa the lowest positive number (no leading zeroes: `1`, `2`, `3`, ...) that produces such a hash.
+
+For example:
+
+* If your secret key is `abcdef`, the answer is `609043`, because the MD5 hash of `abcdef609043` starts with five zeroes (`000001dbbfa...`), and it is the lowest such number to do so.
+* If your secret key is `pqrstuv`, the lowest number it combines with to make an MD5 hash starting with five zeroes is `1048970`; that is, the MD5 hash of `pqrstuv1048970` looks like `000006136ef...`.
+
+Your puzzle answer was `254575`.
+
+\--- Part Two ---
+----------
+
+Now find one that starts with *six zeroes*.
+
+Your puzzle answer was `1038736`.
+
+Both parts of this puzzle are complete! They provide two gold stars: \*\*
+
+At this point, all that is left is for you to [admire your Advent calendar](/2015).
+
+Your puzzle input was `bgvyzdsv`.

2015/day04-ideal_stocking_suffer/src/lib.rs

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+use md5::{Md5, Digest};
+
+fn hash_has_leading_zeroes(input: &str, counter: usize, zeroes: usize) -> bool {
+        let mut hasher = Md5::new();
+        hasher.update(input.to_owned() + &(counter.to_string())[..]);
+        let hash = hasher.finalize();
+        for i in 0..zeroes/2 {
+            if hash[i] != 0 {
+                return false;
+            }
+            if zeroes % 2 == 1 && hash[zeroes/2] >= 16 {
+                return false;
+            }
+        }
+        true
+}
+
+pub fn run(input: &str) -> (usize, usize) {
+    let first = (0..).find(|i| hash_has_leading_zeroes(input, *i, 5)).unwrap();
+
+    let second = (first..).find(|i| hash_has_leading_zeroes(input, *i, 6)).unwrap();
+
+    (first, second)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs::read_to_string;
+
+    fn read_file(name: &str) -> String {
+        read_to_string(name).expect(&format!("Unable to read file: {}", name)[..])
+    }
+
+    #[test]
+    fn test_sample() {
+        let sample_input = read_file("tests/sample_input");
+        let expected = [(609043, 6742839), (1048970, 5714438)];
+        for (idx, input) in sample_input.lines().enumerate() {
+            assert_eq!(run(input), expected[idx]);
+        }
+    }
+
+    #[test]
+    fn test_challenge() {
+        let challenge_input = read_file("tests/challenge_input");
+        for input in challenge_input.lines() {
+            assert_eq!(run(input), (254575, 1038736));
+        }
+    }
+}

2015/day04-ideal_stocking_suffer/tests/challenge_input

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+bgvyzdsv

2015/day04-ideal_stocking_suffer/tests/sample_input

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+abcdef
+pqrstuv