day15 solution

2023/src/day15.rs

@@ -0,0 +1,64 @@
+use aoc_runner_derive::aoc;
+
+fn hash(input: &str) -> usize {
+    let mut cur: usize = 0;
+    for c in input.chars() {
+        cur = ((cur + c as usize) * 17) % 256;
+    }
+    cur
+}
+
+#[aoc(day15, part1)]
+fn part1(input: &str) -> usize {
+    input.trim_end().split(",").map(|t| hash(t)).sum()
+}
+
+#[aoc(day15, part2)]
+fn part2(input: &str) -> usize {
+    let mut boxes: Vec<Vec<(&str, usize)>> = vec![];
+    for _ in 0..256 {
+        boxes.push(vec![]);
+    }
+    for lens in input.trim_end().split(",") {
+        if lens.contains("-") {
+            let parts = lens.split("-").collect::<Vec<&str>>();
+            let h = hash(parts[0]);
+            if let Some(index) = boxes[h].iter().position(|t| t.0 == parts[0]) {
+                boxes[h].remove(index);
+            }
+        } else {
+            let parts = lens.split("=").collect::<Vec<&str>>();
+            let h = hash(parts[0]);
+            let n = (parts[0], parts[1].parse::<usize>().unwrap());
+            if let Some(index) = boxes[h].iter().position(|t| t.0 == parts[0]) {
+                boxes[h][index].1 = n.1;
+            } else {
+                boxes[h].push(n);
+            }
+        }
+    }
+
+    let mut sum = 0;
+    for (box_index, b) in boxes.iter().enumerate() {
+        if b.is_empty() {
+            continue;
+        }
+        for (index, lens) in b.iter().enumerate() {
+            sum += (box_index + 1) * (index + 1) * lens.1;
+        }
+    }
+    sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE_DATA: &'static str = "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7";
+
+    #[test]
+    fn sample_data() {
+        assert_eq!(part1(&SAMPLE_DATA), 1320);
+        assert_eq!(part2(&SAMPLE_DATA), 145);
+    }
+}

2023/src/lib.rs

@@ -14,5 +14,6 @@ mod day11;
 mod day12;
 mod day13;
 mod day14;
+mod day15;
 
 aoc_lib! { year = 2023 }