solution: day 7

src/bin/07.rs

@@ -0,0 +1,81 @@
+use itertools::Itertools;
+
+fn calibrate_equation(
+    fns: &[fn(a: usize, b: usize) -> usize],
+    target: usize,
+    nums: &[usize],
+    acc: usize,
+) -> bool {
+    if nums.is_empty() {
+        return target == acc;
+    }
+
+    if acc > target {
+        return false;
+    }
+
+    fns.iter()
+        .any(|f| calibrate_equation(fns, target, &nums[1..], f(acc, nums[0])))
+}
+
+fn parse_input(input: &str) -> Vec<Vec<usize>> {
+    input
+        .lines()
+        .map(|l| {
+            l.split([' ', ':'])
+                .filter_map(|x| x.parse().ok())
+                .collect_vec()
+        })
+        .collect_vec()
+}
+
+fn sum(a: usize, b: usize) -> usize {
+    a + b
+}
+
+fn prod(a: usize, b: usize) -> usize {
+    a * b
+}
+
+fn concat(a: usize, b: usize) -> usize {
+    a * 10_usize.pow(b.ilog10() + 1) + b
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    parse_input(input)
+        .into_iter()
+        .filter(|n| calibrate_equation(&[sum, prod], n[0], &n[2..], n[1]))
+        .map(|n| n[0])
+        .sum::<usize>()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    parse_input(input)
+        .into_iter()
+        .filter(|n| calibrate_equation(&[sum, prod, concat], n[0], &n[2..], n[1]))
+        .map(|n| n[0])
+        .sum::<usize>()
+        .into()
+}
+
+aoc::solution!(7);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 7)),
+            Some(3749)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 7)),
+            Some(11387)
+        );
+    }
+}