题解 | #岛屿数量#

import java.util.*;


public class Solution {
    /**
     * 判断岛屿数量
     * @param grid char字符型二维数组
     * @return int整型
     */
    public int solve (char[][] grid) {
        if (grid == null) {
            return 0;
        }
        int m = grid.length;
        if (m == 0) {
            return 0;
        }
        int n = grid[0].length;

        int count = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '1') {
                    count++;

                    //将岛屿周围的所有1置0
                    dfs(grid, i, j);
                }
            }
        }
        return count;
    }

    private void dfs(char[][] grid, int i, int j) {
        int m = grid.length;
        int n = grid[0].length;

        grid[i][j] = '0';

        if (i - 1 >= 0 && grid[i - 1][j] == '1') {
            dfs(grid, i - 1, j);
        }

        if (i + 1 < m && grid[i + 1][j] == '1') {
            dfs(grid, i + 1, j);
        }

        if (j - 1 >= 0 && grid[i][j - 1] == '1') {
            dfs(grid, i, j - 1);
        }

        if (j + 1 < n && grid[i][j + 1] == '1') {
            dfs(grid, i, j + 1);
        }
    }
}