0542 - Zero One Matrix

0542 - Zero One Matrix

Given an m x n binary matrix mat, return the distance of the nearest 0 for each cell.

The distance between two adjacent cells is 1.

Examples

Input: mat = [[0,0,0],[0,1,0],[0,0,0]] Output: [[0,0,0],[0,1,0],[0,0,0]]

Input: mat = [[0,0,0],[0,1,0],[1,1,1]] Output: [[0,0,0],[0,1,0],[1,2,1]]

Constraints

m == mat.length n == mat[i].length 1 <= m, n <= 104 1 <= m * n <= 104 mat[i][j] is either 0 or 1. There is at least one 0 in mat.

Java Solution

public class Solution {
    public int[][] updateMatrix(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;
        Queue<int[]> queue = new LinkedList<>();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == 0) queue.offer(new int[] {i, j});
                else matrix[i][j] = Integer.MAX_VALUE;
            }
        }
        int[][] dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
        
        while (!queue.isEmpty()) {
            int[] cell = queue.poll();
            for (int[] d : dirs) {
                int r = cell[0] + d[0];
                int c = cell[1] + d[1];
                if (r < 0 || r >= m || c < 0 || c >= n || 
                    matrix[r][c] <= matrix[cell[0]][cell[1]] + 1) continue;
                queue.add(new int[] {r, c});
                matrix[r][c] = matrix[cell[0]][cell[1]] + 1;
            }
        }
        
        return matrix;
    }
}