public int maxDistance(int[][] grid) { //bfs找到离所有岛屿最远的海洋区域，求这个海洋区域距离所有岛屿中最短的距离

int row = grid.length;

int col = grid[0].length;

int[][] move = {{-1,0}, {1,0}, {0,-1}, {0,1}};

Queue<Point> queue = new ArrayDeque<>(); //用于bfs的队列

for (int i = 0; i < row; i++) {

for (int j = 0; j < col; j++) {

if (grid[i][j] == 1) {

queue.add(new Point(i, j));

}

}

}

if (queue.isEmpty() || queue.size() == row*col) { //全0或全1

return -1;

}

Point point = queue.peek();

while (!queue.isEmpty()) {

point = queue.poll();

for (int i = 0; i < move.length; i++) {

int x = point.x + move[i][0];

int y = point.y + move[i][1];

if (x < 0 || x >= row || y < 0 || y >= col) { //越界

continue;

} else if (grid[x][y] > 0) { //访问过

continue;

}

grid[x][y] = grid[point.x][point.y] + 1;

queue.add(new Point(x, y));

}

}

return grid[point.x][point.y] - 1;

}

/* 定义坐标 */

private class Point {

private int x;

private int y;

public Point(int x, int y) {

this.x = x;

this.y = y;

}

}