P1993 小 K 的农场

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#include<bits/stdc++.h>
using namespace std;const int N=1e4+10,M=5e4+10;
int dist[N],cnt[N],st[N];
int h[N],ne[M],e[M],w[M],idx;
int n,m;void add(int u,int v,int c)
{w[idx]=c,e[idx]=v,ne[idx]=h[u],h[u]=idx++;
}bool spfa()
{memset(dist,0x3f,sizeof dist);dist[0]=0;st[0]=true;queue<int> q;q.push(0);while(q.size()){int t =q.front();q.pop();st[t]=false;for(int i=h[t];~i;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+1) return true;if(!st[j]){q.push(j);st[j]=true;}}}}return false;
}int main()
{ios::sync_with_stdio(0),cin.tie(0);cin>>n>>m;memset(h,-1,sizeof h);for(int i=1;i<=n;i++){add(0,i,0);}while(m--){int op,a,b,c;cin>>op;if(op==1){cin>>a>>b>>c;add(a,b,-c);}else if(op==2){cin>>a>>b>>c;add(b,a,c);}else{cin>>a>>b;add(a,b,0);add(b,a,0);}}if(spfa()){cout<<"No"<<"\n";}else{cout<<"Yes"<<"\n";}return 0;}