1004. 無環圖
#include<iostream>
#include<vector>
using namespace std;
class Solution {
public:
bool isDAG(int n, vector<pair<int, int>>& edges) {
vector<vector<int>> g(n,vector<int>(0));
vector<int> visit(n,0);
for(auto a :edges){
g[a.first].push_back(a.second);
}
for(int i = 0 ;i<n; i++){
if(!DFS(g,visit,i)) return false;
}
return true ;
}
private:
bool DFS(vector<vector<int>> &g ,vector<int> &visit , int i ){
if(visit[i] == -1) return false ;
if(visit[i] == 1) return true;
visit[i]= -1;
for(auto a :g[i]){
if(!DFS(g,visit,a)) return false;
}
visit[i] = 1;
return true ;
}
};