/**

public int numIslands(char[][] grid) {

int num = 0;

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

for (int j = 0; j < grid[0].length; j++) {

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

num++;

dfs(grid, i, j);

}

}

}

return num;

}

// 耗时3ms

/**

private void dfs(char[][] grid, int i, int j) {

if (i < 0 || i >= grid.length || j < 0 || j >= grid[0].length || grid[i][j] != '1') {

return;

}

grid[i][j] = '0';

dfs(grid, i - 1, j);

dfs(grid, i + 1, j);

dfs(grid, i, j - 1);

dfs(grid, i, j + 1);

}

// 耗时6ms

/**

private void bfs(char[][] grid, int i, int j) {

Queue<int[]> queue = new LinkedList<int[]>();

queue.add(new int[] {i, j});

int[] dx = {-1, 1, 0, 0}, dy = {0, 0, - 1, 1};

while (!queue.isEmpty()) {

int[] pos = queue.poll();

int x = pos[0], y = pos[1];

for (int k = 0; k < dx.length; k++) {

int x0 = x + dx[k], y0 = y + dy[k];

if (x0 >= 0 && x0 < grid.length && y0 >= 0 && y0 < grid[0].length && grid[x0][y0] == '1') {

grid[x0][y0] = '0';

queue.add(new int[] {x0, y0});

}

}

}

}