day 20 part 2

src/day20.rs

@@ -0,0 +1,42 @@
+use std::cmp::min;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[aoc_generator(day20)]
+fn parse(input: &str) -> u64 {
+    input.parse().unwrap()
+}
+
+#[aoc(day20, part1)]
+fn part1(min_presents: &u64) -> usize {
+    let min_presents = (min_presents / 10) as usize;
+    let mut house_presents = vec![0; min_presents + 1];
+    for elf in 1..=min_presents {
+        for visited_house in (elf..=min_presents).step_by(elf) {
+            house_presents[visited_house] += elf;
+        }
+    }
+    house_presents
+        .into_iter()
+        .enumerate()
+        .find(|(_, value)| value >= &min_presents)
+        .unwrap()
+        .0
+}
+
+#[aoc(day20, part2)]
+fn part2(min_presents: &u64) -> usize {
+    let min_presents = *min_presents as usize;
+    let mut house_presents = vec![0; min_presents + 1];
+    for elf in 1..=min_presents {
+        for visited_house in (elf..=min(min_presents, elf * 50)).step_by(elf) {
+            house_presents[visited_house] += elf * 11;
+        }
+    }
+    house_presents
+        .into_iter()
+        .enumerate()
+        .find(|(_, value)| value >= &min_presents)
+        .unwrap()
+        .0
+}

src/lib.rs

@@ -12,5 +12,6 @@ mod day16;
 mod day17;
 mod day18;
 mod day19;
+mod day20;
 
 aoc_lib! { year = 2015 }