Google+ Followers

Monday, August 7, 2017

[Leetcode] Number of Islands, Solution

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

[Thoughts]
贪心算法,遍历二维数组,每次只要发现一块land,就BFS其周边,把所有与之连接的land都变成0。BFS完即可island数加一。


[Code]
1:    int numIslands(vector<vector<char>>& grid) {  
2:      int rows = grid.size();  
3:      if(rows == 0) return 0;  
4:      int cols = grid[0].size();  
5:        
6:      int islands = 0;  
7:      for(int i =0; i< rows; i++) {  
8:        for(int j= 0; j< cols; j++) {  
9:          if(grid[i][j] == '0') continue;  
10:          eliminateIsland(grid, i, j, rows, cols);  
11:          islands++;  
12:        }  
13:      }  
14:      return islands;  
15:    }  
16:      
17:    void eliminateIsland(vector<vector<char>>& grid, int x, int y, int& rows, int& cols) {  
18:      if(x<0 || x>=rows) return;  
19:      if(y<0 || y>=cols) return;  
20:      if(grid[x][y] == '0') return;  
21:      grid[x][y] ='0';  
22:        
23:      eliminateIsland(grid, x, y+1, rows, cols);  
24:      eliminateIsland(grid, x, y-1, rows, cols);  
25:      eliminateIsland(grid, x+1, y, rows, cols);  
26:      eliminateIsland(grid, x-1, y, rows, cols);  
27:    }  

Post a Comment