LeetCode : 542. 01 Matrix

// Runtime: 14 ms
// Memory Usage: 46.1 MB
// Ref : https://leetcode.com/submissions/detail/1139015783
class Solution {
    public int[][] updateMatrix(int[][] mat) {
        int[] dx = { 1, -1, 0, 0 };
        int[] dy = { 0, 0, 1, -1 };

        int n = mat.length;
        int m = mat[0].length;
        Queue<Pair<Integer, Integer>> q = new LinkedList<>();

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (mat[i][j] == 1) {
                    mat[i][j] = -1;
                } else {
                    q.add(new Pair(i, j));
                }
            }
        }

        while (!q.isEmpty()) {
            Pair<Integer, Integer> node = q.poll();
            int x = node.getKey();
            int y = node.getValue();

            for (int i = 0; i < 4; i++) {
                int nx = x + dx[i];
                int ny = y + dy[i];
                if (!isRange(n, m, nx, ny)) {
                    continue;
                }
                if (mat[nx][ny] == -1) {
                    mat[nx][ny] = mat[x][y] + 1;
                    q.add(new Pair(nx, ny));
                }
            }
        }

        return mat;
    }

    private boolean isRange(int n, int m, int x, int y) {
        if (x < 0 || x >= n || y < 0 || y >= m) {
            return false;
        }
        return true;
    }
}