LeetCode200. 岛屿数量

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

class Solution {
    public int numIslands(char[][] grid) {
        int res = 0;
        if(grid.length==0 || grid[0].length==0)
            return 0;
        for(int i = 0;i<grid.length;i++)
        {
            for(int j = 0;j<grid[0].length;j++)
            {
                if(grid[i][j]=='1')
                {
                    res++;
                    process(grid, i, j);
                }
            }
        }
        return res;
    }
    public void process(char[][]grid,int i,int j)
    {
        if(!isValid(grid,i,j))
            return;
        if(grid[i][j] != '1')
            return ;
        grid[i][j] = '2';
        process(grid, i-1, j);
        process(grid,i,j+1);
        process(grid, i, j-1);
        process(grid,i+1,j);
    }
    public boolean isValid(char[][] grid,int i,int j)
    {
        return i>=0 && i<grid.length && j>=0 && j<grid[0].length;
    }
}