[2025] Solution for Day 7

Author: kfarnung

2025/src/bin/day07.rs

@@ -0,0 +1,16 @@
+use aoc2025::days::day06::{part1, part2};
+use std::env;
+use std::fs;
+use std::process;
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    if args.len() < 2 {
+        println!("Missing required arguments");
+        process::exit(1);
+    }
+
+    let contents = fs::read_to_string(&args[1]).expect("Something went wrong");
+    println!("Part 1: {}", part1(&contents));
+    println!("Part 2: {}", part2(&contents));
+}

2025/src/days.rs

@@ -4,3 +4,4 @@ pub mod day03;
 pub mod day04;
 pub mod day05;
 pub mod day06;
+pub mod day07;

2025/src/days/day07.rs

@@ -0,0 +1,163 @@
+use std::collections::{HashMap, HashSet, VecDeque};
+
+pub fn part1(contents: &str) -> i64 {
+    let grid = parse_grid(contents);
+    let start = grid[0]
+        .iter()
+        .enumerate()
+        .filter(|(_, c)| *c == &'S')
+        .next()
+        .unwrap();
+    let mut count = 0;
+    let mut queue = VecDeque::new();
+    let mut visited = HashSet::new();
+
+    let start = (0 as usize, start.0);
+    queue.push_back(start);
+    visited.insert(start);
+
+    while !queue.is_empty() {
+        let (y, x) = queue.pop_front().unwrap();
+        if y == grid.len() - 1 {
+            break;
+        }
+
+        match grid[y + 1][x] {
+            '.' => {
+                let next = (y + 1, x);
+                if !visited.contains(&next) {
+                    queue.push_back(next);
+                    visited.insert(next);
+                }
+            }
+            '^' => {
+                let left = (y + 1, x - 1);
+                if !visited.contains(&left) {
+                    queue.push_back(left);
+                    visited.insert(left);
+                }
+                let right = (y + 1, x + 1);
+                if !visited.contains(&right) {
+                    queue.push_back(right);
+                    visited.insert(right);
+                }
+                count += 1;
+            }
+            _ => {
+                panic!("Unexpected character")
+            }
+        }
+    }
+    count
+}
+
+pub fn part2(contents: &str) -> i64 {
+    let grid = parse_grid(contents);
+    let start = grid[0]
+        .iter()
+        .enumerate()
+        .filter(|(_, c)| *c == &'S')
+        .map(|(i, _)| (0 as usize, i))
+        .next()
+        .unwrap();
+    let mut memo = HashMap::new();
+    count_recursive(&grid, start, &mut memo)
+}
+
+fn parse_grid(contents: &str) -> Vec<Vec<char>> {
+    contents
+        .lines()
+        .map(|line| line.chars().collect())
+        .collect()
+}
+
+fn count_recursive(
+    grid: &Vec<Vec<char>>,
+    next: (usize, usize),
+    memo: &mut HashMap<(usize, usize), i64>,
+) -> i64 {
+    if memo.contains_key(&next) {
+        return memo.get(&next).unwrap().clone();
+    }
+
+    if next.0 == grid.len() - 1 {
+        return 1;
+    }
+
+    let mut count = 0;
+    match grid[next.0][next.1] {
+        'S' => {
+            let next = (next.0 + 1, next.1);
+            count += count_recursive(grid, next, memo);
+        }
+        '^' => {
+            let left = (next.0 + 1, next.1 - 1);
+            let right = (next.0 + 1, next.1 + 1);
+            count += count_recursive(grid, left, memo);
+            count += count_recursive(grid, right, memo);
+        }
+        '.' => {
+            let next = (next.0 + 1, next.1);
+            count += count_recursive(grid, next, memo);
+        }
+        _ => {
+            panic!("Unexpected character");
+        }
+    }
+
+    memo.insert(next, count);
+    count
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part1() {
+        let input = vec![
+            ".......S.......",
+            "...............",
+            ".......^.......",
+            "...............",
+            "......^.^......",
+            "...............",
+            ".....^.^.^.....",
+            "...............",
+            "....^.^...^....",
+            "...............",
+            "...^.^...^.^...",
+            "...............",
+            "..^...^.....^..",
+            "...............",
+            ".^.^.^.^.^...^.",
+            "...............",
+        ];
+
+        assert_eq!(part1(&input.join("\n")), 21);
+    }
+
+    #[test]
+    fn test_part2() {
+        let input = vec![
+            ".......S.......",
+            "...............",
+            ".......^.......",
+            "...............",
+            "......^.^......",
+            "...............",
+            ".....^.^.^.....",
+            "...............",
+            "....^.^...^....",
+            "...............",
+            "...^.^...^.^...",
+            "...............",
+            "..^...^.....^..",
+            "...............",
+            ".^.^.^.^.^...^.",
+            "...............",
+        ];
+
+        assert_eq!(part2(&input.join("\n")), 40);
+    }
+}

2025/tests/day07.rs

@@ -0,0 +1,13 @@
+use aoc2025::days::day07::{part1, part2};
+
+#[test]
+fn test_part1() {
+    let content = std::include_str!("../../private/inputs/2025/day07.txt");
+    assert_eq!(part1(&content), 1626);
+}
+
+#[test]
+fn test_part2() {
+    let content = std::include_str!("../../private/inputs/2025/day07.txt");
+    assert_eq!(part2(&content), 48989920237096);
+}