给你一个由 '1'（陆地）和 '0'（水）组成的的二维网格，请你计算网格中岛屿的数量。

岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。

此外，你可以假设该网格的四条边均被水包围。

示例 1：

输入：

复制
1grid = [
2  ["1","1","1","1","0"],
3  ["1","1","0","1","0"],
4  ["1","1","0","0","0"],
5  ["0","0","0","0","0"]
6]

输出： 1

示例 2：

输入：

复制
1grid = [
2  ["1","1","0","0","0"],
3  ["1","1","0","0","0"],
4  ["0","0","1","0","0"],
5  ["0","0","0","1","1"]
6]

输出： 3

提示：

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 300
• grid[i][j] 的值为 '0' 或 '1'

复制
1/**
2 * @param {character[][]} grid
3 * @return {number}
4 */
5var numIslands = function(grid) {
6
7};