题目描述
blablabla
C++ 代码
#include <iostream>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;
const int N = 2010;
const int M = 10010;
int h[N],e[M],ne[M],w[M],idx,cnt[N],dist[N];
int n,m;
bool st[N];
void add(int a,int b,int c){
e[idx] = b;
ne[idx] = h[a];
w[idx] = c;
h[a] = idx++;
}
bool spfa(){
queue<int> q;
for(int i = 1;i <= n;++i){
st[i] = true;
q.push(i);
}
while(!q.empty()){
auto t = q.front();
q.pop();
st[t] = false;
for(int i = h[t];i != -1;i = ne[i]){
int j = e[i];
if(dist[j] > dist[t] + w[i]){
dist[j] = dist[t] + w[i];
cnt[j] = cnt[t] + 1;
if(cnt[j] >= n) return true;
if(!st[j]){
q.push(j);
st[j] = true;
}
}
}
}
return false;
}
int main(){
memset(h,-1,sizeof h);
cin >> n >> m;
while(m--){
int a,b,c;
cin >> a >> b >> c;
add(a,b,c);
}
if(spfa()) cout << "Yes" <<endl;
else cout << "No" <<endl;
return 0;
}