岛屿数量

问题

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：grid = [
  ["1","1","1","1","0"],
  ["1","1","0","1","0"],
  ["1","1","0","0","0"],
  ["0","0","0","0","0"]
]
输出：1
示例 2：

输入：grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
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'

答案

var numIslands = function(grid) {
    const row=grid.length;
    const column=grid[0].length;
    function dfs(i,j){
        if(i<0||j<0||i>=row||j>=column||grid[i][j]!=='1') return;
        grid[i][j]='2';
        dfs(i,j-1);
        dfs(i,j+1);
        dfs(i-1,j);
        dfs(i+1,j);
    }
    let res=0;
    for(let i=0;i<row;i++){
        for(let j=0;j<column;j++){
            if(grid[i][j]==='1'){
                dfs(i,j);
                res++;
            }
        }
    }
    return res;
};

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