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);}
}