P1038 [NOIP2003 提高组] 神经网络

https://www.luogu.com.cn/problem/P1038

#include <iostream>
#include<queue> 
#include <vector>
#include <cstring>
using namespace std;
 const int N=104, M=1e5;
 int nxt[M],go[M],hd[N],w[M],all=1;
 int n,m,U[N],C[N];
 int in[N],out[N];
 
 void add_(int x,int y,int z){
 	nxt[++all]=hd[x]; hd[x]=all;
 	go[all]=y; w[all]=z;
 }
void solve(){
 	int i,x;
 	queue<int> q;
 	
 	for(i=1;i<=n;i++) 
	 if(in[i]==0) q.push(i);
 	
	 while(q.empty()==0){
 		x=q.front();
		q.pop();
 		if(C[x]<0) continue ;
 		
 		for(i=hd[x];i;i=nxt[i]){
 			int y=go[i],z=w[i];
 			--in[y];
 			
 			if(C[x]>0) C[y]+=z*C[x];
 			if(in[y]==0) q.push(y); 
		 }
	 }
	 int fg=0;
	 for(i=1;i<=n;i++){
	 	if(C[i]>0&& out[i]==0) {fg=1; break;}
	 }
	 if(fg==0){
	 	cout<<"NULL\n";return;
	 }
	 for(i=1;i<=n;i++){
	 	if(out[i]==0&&C[i]>0) cout<<i<<' '<<C[i]<<endl;
	 }
 }
 signed main(){
 	int i;
 	cin>>n>>m;
 	for(i=1;i<=n;i++){
 		cin>>C[i]>>U[i]; if(C[i]==0) C[i]-=U[i];
 	}
 	for(i=1;i<=m;i++){
 		int x,y,z;
 		cin>>x>>y>>z; add_(x,y,z);
 		out[x]++,in[y]++;
 	}
	solve();
 }