My code gets WA but I don't know why
/*
* main.cpp
*
* Created on: Feb 20, 2013
* Author: Sony
*/
#include <iostream>
#include <vector>
using namespace std;
vector<vector<int> > all ;
bool vis[10001];
bool DFS(int cur){
//cout << cur << endl ;
if(vis[cur] == 1)
return 0 ;
vis[cur] = 1;
for (int i = 0; i < all[cur].size(); ++i) {
DFS(all[cur][i]);
}
return 1 ;
}
int main(){
memset(vis,0,sizeof(vis));
int m,n ;
scanf("%d%d",&m,&n);
all.resize(m);
int a,b;
for (int i = 0; i < n; ++i) {
scanf("%d%d",&a,&b);
all[a-1].push_back(b-1);
}
if(m != n-1)
printf("NO\n");
return 0;
bool answer = DFS(0);
for (int i = 0; i < all.size(); ++i) {
if(vis[i]==0)
answer = 0 ;
}
if(answer==0)
printf("NO\n");
else
printf("YES\n");
return 0;
}
