Day 25 solved!!!

data/examples/25.txt

@@ -0,0 +1,39 @@
+#####
+.####
+.####
+.####
+.#.#.
+.#...
+.....
+
+#####
+##.##
+.#.##
+...##
+...#.
+...#.
+.....
+
+.....
+#....
+#....
+#...#
+#.#.#
+#.###
+#####
+
+.....
+.....
+#.#..
+###..
+###.#
+###.#
+#####
+
+.....
+.....
+.....
+#....
+#.#..
+#.#.#
+#####

src/bin/25.rs

@@ -1,7 +1,39 @@
+use itertools::iproduct;
+
 advent_of_code::solution!(25);
 
+fn parse(input: &str) -> Option<(Vec<[i64; 5]>, Vec<[i64; 5]>)> {
+    let mut keys = vec![];
+    let mut locks = vec![];
+    let mut buffer = [0; 5];
+    for grid in input.split("\n\n") {
+        for row in grid.split_whitespace() {
+            for (i, cell) in row.trim().chars().enumerate() {
+                buffer[i] += if cell == '#' { 1 } else { -1 };
+            }
+        }
+        // as top row is filled
+        // if grid.chars().take(5).all(|c| c == '#') {
+        if grid.chars().next() == Some('#') {
+            locks.push(buffer);
+        } else {
+            keys.push(buffer);
+        }
+        buffer.fill(0);
+    }
+    Some((keys, locks))
+}
+
 pub fn part_one(input: &str) -> Option<u64> {
-    None
+    let (keys, locks) = dbg!(parse(input))?;
+
+    let mut count = 0;
+    for (key, lock) in iproduct!(keys, locks) {
+        if key.iter().zip(lock).all(|(a, b)| a + b <= 0) {
+            count += 1;
+        }
+    }
+    Some(count)
 }
 
 pub fn part_two(input: &str) -> Option<u64> {
@@ -15,7 +47,7 @@ mod tests {
     #[test]
     fn test_part_one() {
         let result = part_one(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(3));
     }
 
     #[test]