Leetcode 542 01矩阵 图的按距离遍历

 

　　按距离进行 BFS 即可，JAVA:

int[][] dir = new int[][]{{1, 0}, {-1, 0}, {0, 1}, {0, -1}};

    public final int[][] updateMatrix(int[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) return new int[0][0];
        int xLen = matrix.length, yLen = matrix[0].length;
        Set<Long> set = new HashSet<Long>();
        Queue<int[]> queue = new LinkedList<int[]>();
        for (int i = 0; i < xLen; i++) {
            for (int j = 0; j < yLen; j++) {
                if (matrix[i][j] == 0) {
                    queue.add(new int[]{i, j});
                    set.add(((long) i) << 32 | (long) j);
                }
                ;
            }
        }
        int currentNum = 1;
        while (queue.size() > 0) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                int[] current = queue.poll();
                int x = current[0], y = current[1];
                for (int j = 0; j < 4; j++) {
                    int dX = x + dir[j][0], dY = y + dir[j][1];
                    long key = ((long) dX) << 32 | (long) dY;
                    if (dX >= xLen || dX < 0 || dY >= yLen || dY < 0 || set.contains(key)) continue;
                    matrix[dX][dY] = currentNum;
                    queue.add(new int[]{dX, dY});
                    set.add(key);
                }
            }
            currentNum++;
        }
        return matrix;
    }

　　JS，在构造二维矩阵时要慎用 fill 方法，fill 方法中如果填充内容是对象，所有元素将指向同一对象:

/**
 * @param {number[][]} matrix
 * @return {number[][]}
 */
var updateMatrix = function (matrix) {
    if (!matrix || matrix.length == 0 || matrix[0].length == 0) return matrix;
    let dir = [[1, 0], [-1, 0], [0, 1], [0, -1]];
    let queue = [];
    let xLen = matrix.length, yLen = matrix[0].length;
    let his = new Array(xLen);
    for (let i = 0; i < xLen; i++) his[i] = new Array(yLen).fill(0);
    for (let i = 0; i < xLen; i++) {
        for (let j = 0; j < yLen; j++) {
            if (matrix[i][j] == 0) {
                queue.push([i, j]);
                his[i][j] = 1;
            }
        }
    }
    let currentNum = 1;
    while (queue.length > 0) {
        let currentLen = queue.length;
        for (let i = 0; i < currentLen; i++) {
            let currentNode = queue.shift();
            let x = currentNode[0], y = currentNode[1];
            for (let j = 0; j < 4; j++) {
                let dX = x + dir[j][0], dY = y + dir[j][1];
                if (dX < 0 || dX >= xLen || dY < 0 || dY >= yLen || his[dX][dY] == 1) continue;
                matrix[dX][dY] = currentNum;
                his[dX][dY] = 1;
                queue.push([dX, dY]);
            }
        }
        currentNum++;
    }
    return matrix;
}