From 3019634d8fc56ad5ffb2858ff28eadb555c2e405 Mon Sep 17 00:00:00 2001
From: Himangshu Saikia <himangshu.saikia.iitg@gmail.com>
Date: Sun, 15 Dec 2024 09:01:34 +0100
Subject: [PATCH] 2024_15

---
 src/bin/2024_15/main.rs | 168 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 168 insertions(+)
 create mode 100644 src/bin/2024_15/main.rs

diff --git a/src/bin/2024_15/main.rs b/src/bin/2024_15/main.rs
new file mode 100644
index 0000000..5fdc1f5
--- /dev/null
+++ b/src/bin/2024_15/main.rs
@@ -0,0 +1,168 @@
+use aoc::{common, grid::Grid};
+use itertools::Itertools;
+
+fn get_dir(ch: char) -> (i32, i32) {
+    if ch == '>' {
+        (0, 1)
+    } else if ch == 'v' {
+        (1, 0)
+    } else if ch == '<' {
+        (0, -1)
+    } else if ch == '^' {
+        (-1, 0)
+    } else {
+        panic!("Invalid char {}", ch);
+    }
+}
+
+fn possible_steps(map: &Grid<char>, pos: &(usize, usize), dir: char) -> usize {
+    let sym = map.get(pos);
+    if sym == '.' || sym == '#' {
+        return 0;
+    }
+    let dir_xy = get_dir(dir);
+
+    if let Some(idx) = map.cell_in_direction(pos, &dir_xy) {
+        if map.get(&idx) == '#' {
+            return 0;
+        }
+        if map.get(&idx) == '.' {
+            return 1 + possible_steps(map, &idx, dir);
+        }
+        if map.get(&idx) == '[' {
+            if dir == '^' || dir == 'v' {
+                return possible_steps(map, &idx, dir).min(possible_steps(
+                    map,
+                    &(idx.0, idx.1 + 1),
+                    dir,
+                ));
+            }
+            return possible_steps(map, &idx, dir);
+        }
+        if map.get(&idx) == ']' {
+            if dir == '^' || dir == 'v' {
+                return possible_steps(map, &idx, dir).min(possible_steps(
+                    map,
+                    &(idx.0, idx.1 - 1),
+                    dir,
+                ));
+            }
+            return possible_steps(map, &idx, dir);
+        }
+        if map.get(&idx) == 'O' {
+            return possible_steps(map, &idx, dir);
+        }
+    }
+    0
+}
+
+fn push(map: &mut Grid<char>, pos: (usize, usize), dir: char, steps: usize) -> bool {
+    let sym = map.get(&pos);
+    if sym == '.' || sym == '#' {
+        return false;
+    }
+    if steps == 0 {
+        return true;
+    }
+    let dir_xy = get_dir(dir);
+
+    if let Some(idx) = map.cell_in_direction(&pos, &dir_xy) {
+        if map.get(&idx) == '#' {
+            return false;
+        }
+        if map.get(&idx) == '.' {
+            let sym = map.get(&pos);
+            map.set(&idx, sym);
+            map.set(&pos, '.');
+            return push(map, idx, dir, steps - 1);
+        }
+        if map.get(&idx) == '[' {
+            if dir == '^' || dir == 'v' {
+                if push(map, idx, dir, steps) && push(map, (idx.0, idx.1 + 1), dir, steps) {
+                    return push(map, pos, dir, steps);
+                }
+            } else if push(map, idx, dir, steps) {
+                return push(map, pos, dir, steps);
+            }
+        }
+        if map.get(&idx) == ']' {
+            if dir == '^' || dir == 'v' {
+                if push(map, idx, dir, steps) && push(map, (idx.0, idx.1 - 1), dir, steps) {
+                    push(map, pos, dir, steps);
+                }
+            } else if push(map, idx, dir, steps) {
+                return push(map, pos, dir, steps);
+            }
+        }
+        if map.get(&idx) == 'O' && push(map, idx, dir, steps) {
+            return push(map, pos, dir, steps);
+        }
+    }
+
+    true
+}
+
+fn solve<const PART: usize>(input: &str) -> usize {
+    let batches: Vec<&str> = input.split("\n\n").collect();
+    let transformed: String = if PART == 2 {
+        batches[0]
+            .lines()
+            .map(|l| {
+                l.chars()
+                    .map(|c| {
+                        if c == '.' {
+                            ".."
+                        } else if c == '@' {
+                            "@."
+                        } else if c == 'O' {
+                            "[]"
+                        } else {
+                            "##"
+                        }
+                    })
+                    .join("")
+            })
+            .join("\n")
+    } else {
+        batches[0].to_string()
+    };
+    let mut map = Grid::from_str(&transformed, |c| c);
+    let commands = batches[1];
+
+    //map.print();
+
+    for ch in commands.chars() {
+        if ch == '\n' {
+            continue;
+        }
+
+        let pos = map.positions('@');
+        let ps = possible_steps(&map, &pos[0], ch);
+        push(&mut map, pos[0], ch, ps.min(1));
+        push(&mut map, pos[0], ch, ps.min(1));
+    }
+
+    let mut ans = 0;
+    for pos in map.positions(if PART == 1 { 'O' } else { '[' }) {
+        ans += pos.0 * 100 + pos.1
+    }
+    ans
+}
+fn main() {
+    let input = common::get_input();
+    println!("{input:?}");
+    common::timed(&input, solve::<1>, true);
+    common::timed(&input, solve::<2>, false);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_samples() {
+        let sample_input = "##########\n#..O..O.O#\n#......O.#\n#.OO..O.O#\n#..O@..O.#\n#O#..O...#\n#O..O..O.#\n#.OO.O.OO#\n#....O...#\n##########\n\n<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^\nvvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v\n><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<\n<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^\n^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><\n^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^\n>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^\n<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>\n^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>\nv^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^";
+        assert_eq!(solve::<1>(sample_input), 10092);
+        assert_eq!(solve::<2>(sample_input), 9021);
+    }
+}