leetcode200.岛屿数量

leetcode200.岛屿数量

题目

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。

用例

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

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

求解

/**
 * @param {character[][]} grid
 * @return {number}
 */
var numIslands = function(grid) {
    let res = 0
    for(let i=0;i<grid.length;i++){
        for(let j=0;j<grid[0].length;j++){
            //发现未被访问过，且是陆地的部分,进行深度优先遍历，沉没陆地
            if(grid[i][j]==1){
                res++
                dfs(i,j)
            }
        }
    }
    return res

    //深度优先遍历
    function dfs(i,j){
        if(grid[i][j]==0){
            return
        }
        //沉没当前陆地
        grid[i][j]=0
        if(i-1>=0) dfs(i-1,j)
        if(j-1>=0) dfs(i,j-1)
        if(i+1<grid.length) dfs(i+1,j)
        if(j+1<grid[0].length) dfs(i,j+1)
    }
};