leetcode200

解题思路

去年没写出来的每日一题，今年来还愿

代码

class Solution {
       public int numIslands(char[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        int ans = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '1') {
                    ++ans;
                    dfs(grid, i, j, ans);
                }
            }
        }
        return ans;
    }

    public int dfs(char[][] grid, int i, int j, int ans) {
        grid[i][j] = (char) (ans+'1');
        if (i > 0 && grid[i - 1][j] == '1') {
            grid[i - 1][j] = grid[i][j];
            dfs(grid, i - 1, j, ans);
        }
        if (j > 0 && grid[i][j - 1] == '1') {
            grid[i][j - 1] = grid[i][j];
            dfs(grid, i , j-1, ans);
        }
        if (i +1 < grid.length && grid[i + 1][j] == '1') {
            grid[i + 1][j] = grid[i][j];
            dfs(grid, i + 1, j, ans);
        }
        if (j +1 < grid[0].length && grid[i][j+1] == '1') {
            grid[i][j+1] = grid[i][j];
            dfs(grid, i , j+1, ans);
        }
        return ans;
    }
}