题目链接:
https://cpc.csgrandeur.cn/csgoj/problemset/problem?pid=1135

这个题的代码真不懂，求助大家

#include<cstdio>
#include<queue>
#include<iostream>
#include<vector>
#include<map>
#include<cstring>
#include<string>
#include<set>
#include<stack>
#include<algorithm>
#define cle(a) memset(a,0,sizeof(a))
#define inf(a) memset(a,0x3f,sizeof(a))
#define ll long long
#define Rep(i,a,n) for(int i=a;i<=n;i++)
using namespace std;
#define INF2 9223372036854775807ll
const int INF = ( 2e9 ) + 2;
const ll maxn = 1e5+10;
int d[maxn],a[maxn],b[maxn],In[maxn];
vector<int> g[maxn];
const int mod = 1e9+7;
ll topsort(int n)
{
    ll ans=0;
    priority_queue<int> q;
    for(int i=1;i<=n;i++)
    {
        if(In[i]==0)
        {
            q.push(i);
        }
    }
    while(!q.empty())
    {
        int u=q.top();q.pop();
        d[u]=(d[u]+a[u])%mod;
        for(int i=0,L=g[u].size();i<L;i++)
        {
            int v=g[u][i];
            In[v]--;
            d[v] = (d[u]+d[v])%mod;
            if(In[v]==0)
            q.push(v);
            ans = (ans+1LL*d[u]*b[v])%mod;
        }
    }
    return ans%mod;
}
int main()
{
    int n,m;
    while(~scanf("%d%d",&n,&m))
    {
        for(int i=1;i<=n;i++)g[i].clear();
        memset(In,0,sizeof(In));
        memset(d,0,sizeof(d));
        for(int i=1;i<=n;i++)
        scanf("%d%d",&a[i],&b[i]);
        for(int i=0;i<m;i++)
        {
            int u,v;
            scanf("%d%d",&u,&v);
            g[u].push_back(v);
            In[v]++;
        }
        ll ans=topsort(n);
        cout<<ans<<endl;
    }
}