The Preliminary Contest for ICPC Asia Nanjing 2019 H. Holy Grail

题目链接：https://nanti.jisuanke.com/t/41305

题目说的很明白。。。只需要反向跑spfa然后输入-dis，然后添-dis的一条边就好了。。。

---

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <queue>
 #include <map>
 #include <cmath>
 #include <iomanip>
 using namespace std;

 typedef long long LL;
 #define inf 1e14
 #define rep(i, j, k) for (int i = (j); i <= (k); i++)
 #define rep__(i, j, k) for (int i = (j); i < (k); i++)
 #define per(i, j, k) for (int i = (j); i >= (k); i--)
 #define per__(i, j, k) for (int i = (j); i > (k); i--)

 const int N = ;
 int head[N];
 int cnt;
 bool vis[N];
 LL dis[N];
 queue<int > que;
 int n,m;

 struct Edge{
     int to;
     LL w;
     int next;
 }e[];

 void add(int u,int v,LL w){
     e[cnt].to = v;
     e[cnt].w = w;
     e[cnt].next = head[u];
     head[u] = cnt++;
 }

 void spfa(int s){

     while(!que.empty()) que.pop();
     rep__(i,,n){
         vis[i] = false;
         dis[i] = inf;
     }

     dis[s] = ;
     que.push(s);

     int u,v;
     LL w;
     while(!que.empty()){
         u = que.front();
  //       cout << "u " << u << endl;
         que.pop();
         vis[u] = false;
         for(int o = head[u]; ~o; o = e[o].next){
             v = e[o].to;
             w = e[o].w;
             if(dis[v] > dis[u] + w){
                 dis[v] = dis[u] + w;
                 if(!vis[v]){
                     vis[v] = true;
                     que.push(v);
                 }
             }
         }
     }
 }

 int main(){

     int T;
     scanf("%d",&T);

     int u,v;
     LL w;
     rep(o,,T){
         scanf("%d%d",&n,&m);

         rep__(i,,n) head[i] = -;
         cnt = ;

         rep(i,,m){
             scanf("%d%d%lld",&u,&v,&w);
             add(u,v,w);
         }

         // rep__(i,o,n){
         //     cout << " u " << i << endl;

         //     for(int  o = head[i]; ~o; o = e[o].next){
         //         cout << e[o].to << " " << e[o].w << endl;
         //     }
         // }

         rep(i,,){
             scanf("%d%d",&u,&v);
             spfa(v);
             printf("%lld\n",-dis[u]);
             add(u,v,-dis[u]);
         }
     }

     getchar();getchar();
     return ;
 }