Leetcode 200. Number of Islands

Posted 2020-07-09 琴影

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:

11110 
11010 
11000 
00000

Answer: 1

Example 2:

11000 
11000 
00100 
00011

Answer: 3

 

 1 class Solution {
 2 public:
 3     int numIslands(vector<vector<char>>& grid) {
 4         int many = 0;
 5         if(grid.empty() || grid[0].empty())
 6             return many;
 7         //void dfs(vector<vector<char>> &grid,int i, int j, int n, int m);
 8         int n = grid.size();
 9         int m = grid[0].size();
10         for(int i = 0; i < n; i++){
11             for(int j = 0; j < m; j++){
12                 if(grid[i][j] == \'1\'){
13                     dfs(grid,i,j,n,m);
14                     many++;
15                 }
16             }
17         }
18         return many;
19     }
20     void dfs(vector<vector<char>>& grid,int i, int j, int n, int m)
21     {
22         grid[i][j] = \'0\';
23         if((i-1) >= 0 && grid[i-1][j] == \'1\')
24             dfs(grid, i-1, j, n, m);
25         if((i+1) < n && grid[i+1][j] == \'1\')
26             dfs(grid, i+1, j, n, m); 
27         if((j-1) >= 0 && grid[i][j-1] == \'1\')
28             dfs(grid, i, j-1, n, m);
29         if((j+1) < m && grid[i][j+1] == \'1\')
30             dfs(grid, i, j+1, n, m);
31     }
32 };

View Code