【刷题-LeetCode】200 Number of Islands
- 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:
Input: grid = [
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]
]
Output: 1
Example 2:
Input: grid = [
["1","1","0","0","0"],
["1","1","0","0","0"],
["0","0","1","0","0"],
["0","0","0","1","1"]
]
Output: 3
解1 bfs
class Solution {
public:
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
bool valid(int x, int y, int m, int n){
if(x < 0 || x >= m || y < 0 || y >= n)return false;
return true;
}
int numIslands(vector<vector<char>>& grid) {
if(grid.size() == 0)return 0;
vector<vector<bool>> vis(grid.size(), vector<bool>(grid[0].size(), false));
int ans = 0;
for(int i = 0; i < grid.size(); ++i){
for(int j = 0; j < grid[0].size(); ++j){
if(vis[i][j] == false && grid[i][j] == '1'){
ans++;
bfs(grid, vis, i, j);
//dfs(grid, vis, i, j);
}
}
}
return ans;
}
void bfs(vector<vector<char>>& grid, vector<vector<bool>>& vis,
int x, int y){
queue<pair<int, int>>q;
q.push(make_pair(x,y));
vis[x][y] = true;
while(!q.empty()){
int tmpx = q.front().first, tmpy = q.front().second;
q.pop();
for(int i = 0; i < 4; ++i){
int tmpxx = tmpx + dx[i], tmpyy = tmpy + dy[i];
if(valid(tmpxx, tmpyy, grid.size(), grid[0].size())
&& !vis[tmpxx][tmpyy] && grid[tmpxx][tmpyy]=='1'){
q.push(make_pair(tmpxx, tmpyy));
vis[tmpxx][tmpyy] = true;
}
}
}
}
};
解2 dfs
void dfs(vector<vector<char>>& grid, vector<vector<bool>>& vis,
int x, int y){
vis[x][y] = true;
for(int i = 0; i < 4; ++i){
int tmpx = x + dx[i], tmpy = y + dy[i];
if(valid(tmpx, tmpy, grid.size(), grid[0].size())
&& !vis[tmpx][tmpy] && grid[tmpx][tmpy] == '1'){
dfs(grid, vis, tmpx, tmpy);
}
}
}
作者:Vinson
-------------------------------------------
个性签名:只要想起一生中后悔的事,梅花便落满了南山
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