README.md

994. Rotting Oranges

In a given grid, each cell can have one of three values:

• the value 0 representing an empty cell;
• the value 1 representing a fresh orange;
• the value 2 representing a rotten orange.

Every minute, any fresh orange that is adjacent (4-directionally) to a rotten orange becomes rotten.

Return the minimum number of minutes that must elapse until no cell has a fresh orange. If this is impossible, return -1 instead.

Example 1:

Input: [[2,1,1],[1,1,0],[0,1,1]]
Output: 4

Example 2:

Input: [[2,1,1],[0,1,1],[1,0,1]]
Output: -1
Explanation: The orange in the bottom left corner (row 2, column 0) is never rotten, because rotting only happens 4-directionally.

Example 3:

Input: [[0,2]]
Output: 0
Explanation: Since there are already no fresh oranges at minute 0, the answer is just 0.

Note:

1. 1 <= grid.length <= 10
2. 1 <= grid[0].length <= 10
3. grid[i][j] is only 0, 1, or 2.

Solutions (Rust)

1. Simulation

impl Solution {
    pub fn oranges_rotting(grid: Vec<Vec<i32>>) -> i32 {
        let mut prev = grid;

        for minute in 0..59 {
            let mut no_fresh = true;
            let mut new = prev.clone();

            for j in 0..prev.len() {
                for k in 0..prev[0].len() {
                    match prev[j][k] {
                        1 => no_fresh = false,
                        2 => {
                            if j > 0 && prev[j - 1][k] == 1 {
                                new[j - 1][k] = 2;
                            }
                            if k > 0 && prev[j][k - 1] == 1 {
                                new[j][k - 1] = 2;
                            }
                            if j < prev.len() - 1 && prev[j + 1][k] == 1 {
                                new[j + 1][k] = 2;
                            }
                            if k < prev[0].len() - 1 && prev[j][k + 1] == 1 {
                                new[j][k + 1] = 2;
                            }
                        },
                        _ => (),
                    };
                }
            }

            if no_fresh {
                return minute;
            }

            prev = new;
        }

        -1
    }
}