Leetcode|Number of Islands

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

这个题是典型的搜索问题。记录好搜索过的地方就可以迎刃而解。

void search(vector<vector<char>>& grid,int r,int c){
if(r<0||r>=grid.size()||c<0||c>=grid[0].size()||grid[r][c]!='1'){
return;
}

grid[r][c]='V';

search(grid,r-1,c);
search(grid,r+1,c);
search(grid,r,c-1);
search(grid,r,c+1);
}

int numIslands(vector<vector<char>>& grid) {
int res=0;
for(int i=0;i<grid.size();i++){
for(int j=0;j<grid[0].size();j++){
if(grid[i][j]!='1') continue;
res++;
search(grid,i,j);
}
}
return res;
}