[LeetCode] Number of Islands

本文轉載自查看原文 2015-04-08 12:37 2918 DFS/ C++/ Leetcode/ Algorithm

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Answer: 1

Example 2:

Answer: 3

沒什么，DFS就好了。

 1 class Solution {
 2 public:
 3     void dfs(vector<vector<char>> &grid, int x, int y) {
 4         if (x < 0 || x >= grid.size()) return;
 5         if (y < 0 || y >= grid[0].size()) return;
 6         if (grid[x][y] != '1') return;
 7         grid[x][y] = 'X';
 8         dfs(grid, x + 1, y);
 9         dfs(grid, x - 1, y);
10         dfs(grid, x, y + 1);
11         dfs(grid, x, y - 1);
12     }
13     
14     int numIslands(vector<vector<char>> &grid) {
15         if (grid.empty() || grid[0].empty()) return 0;
16         int N = grid.size(), M = grid[0].size();
17         int cnt = 0;
18         for (int i = 0; i < N; ++i) {
19             for (int j = 0; j < M; ++j) {
20                 if (grid[i][j] == '1') {
21                     dfs(grid, i, j);
22                     ++cnt;
23                 }
24             }
25         }
26         return cnt;
27     }
28 };

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