Number of Islands
Number of Islands
题目
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
思路
DFS
解题
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29class Solution {
public:
int numIslands(vector<vector<char>>& grid) {
if(grid.empty())
return 0;
int m=grid.size();
int n=grid[0].size();
int cnt=0;
for(int i=0;i<m;i++){
for(int j=0;j<n;j++){
if(grid[i][j]=='1'){
dfs(grid,i,j);
cnt++;
}
}
}
return cnt;
}
void dfs(vector<vector<char>>&grid, int i,int j){
if(i<0 || i>=grid.size() || j<0 || j>=grid[0].size()) return;
if(grid[i][j]!='1') return;
grid[i][j]='X';
dfs(grid,i-1,j);
dfs(grid,i+1,j);
dfs(grid,i,j-1);
dfs(grid,i,j+1);
}
};
python版1
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27class Solution:
# @param {character[][]} grid
# @return {integer}
def numIslands(self, grid):
if len(grid)==0 or len(grid[0])==0:
return 0
m=len(grid)
n=len(grid[0])
cnt=0
for i in range(m):
for j in range(n):
if grid[i][j]=='1':
self.dfs(grid,i,j)
cnt+=1
return cnt
def dfs(self,grid,i,j):
if i<0 or i>=len(grid) or j<0 or j>=len(grid[0]):
return
if grid[i][j]!='1':
return
grid[i][j]='X'
self.dfs(grid,i+1,j)
self.dfs(grid,i-1,j)
self.dfs(grid,i,j+1)
self.dfs(grid,i,j-1)