题目

法1：岛屿数量

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

        return res;
    }

    public void dfs(int i, int j, char[][] grid, int[][] used, int m, int n) {
        if (i < 0 || i >= m 
                || j < 0 || j >= n 
                || grid[i][j] == '0' || used[i][j] == 1) {
            return;
        }
        used[i][j] = 1;

        dfs(i - 1, j, grid, used, m, n); 
        dfs(i + 1, j, grid, used, m, n);
        dfs(i, j - 1, grid, used, m, n); 
        dfs(i, j + 1, grid, used, m, n);
    }
}