48 lines
No EOL
2.1 KiB
Text
48 lines
No EOL
2.1 KiB
Text
\--- Day 20: Infinite Elves and Infinite Houses ---
|
|
----------
|
|
|
|
To keep the Elves busy, Santa has them deliver some presents by hand, door-to-door. He sends them down a street with infinite houses numbered sequentially: `1`, `2`, `3`, `4`, `5`, and so on.
|
|
|
|
Each Elf is assigned a number, too, and delivers presents to houses based on that number:
|
|
|
|
* The first Elf (number `1`) delivers presents to every house: `1`, `2`, `3`, `4`, `5`, ....
|
|
* The second Elf (number `2`) delivers presents to every second house: `2`, `4`, `6`, `8`, `10`, ....
|
|
* Elf number `3` delivers presents to every third house: `3`, `6`, `9`, `12`, `15`, ....
|
|
|
|
There are infinitely many Elves, numbered starting with `1`. Each Elf delivers presents equal to *ten times* his or her number at each house.
|
|
|
|
So, the first nine houses on the street end up like this:
|
|
|
|
```
|
|
House 1 got 10 presents.
|
|
House 2 got 30 presents.
|
|
House 3 got 40 presents.
|
|
House 4 got 70 presents.
|
|
House 5 got 60 presents.
|
|
House 6 got 120 presents.
|
|
House 7 got 80 presents.
|
|
House 8 got 150 presents.
|
|
House 9 got 130 presents.
|
|
|
|
```
|
|
|
|
The first house gets `10` presents: it is visited only by Elf `1`, which delivers `1 * 10 = 10` presents. The fourth house gets `70` presents, because it is visited by Elves `1`, `2`, and `4`, for a total of `10 + 20 + 40 = 70` presents.
|
|
|
|
What is the *lowest house number* of the house to get at least as many presents as the number in your puzzle input?
|
|
|
|
Your puzzle answer was `665280`.
|
|
|
|
\--- Part Two ---
|
|
----------
|
|
|
|
The Elves decide they don't want to visit an infinite number of houses. Instead, each Elf will stop after delivering presents to `50` houses. To make up for it, they decide to deliver presents equal to *eleven times* their number at each house.
|
|
|
|
With these changes, what is the new *lowest house number* of the house to get at least as many presents as the number in your puzzle input?
|
|
|
|
Your puzzle answer was `705600`.
|
|
|
|
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 `29000000`. |