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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();
 }