Extended Traffic LightOJ - 1074

题目链接：https://vjudge.net/problem/LightOJ-1074

思路：(busyness of destination - busyness of source)³ 可能会是负值，那么可能出现负环，

需要SFPA来解决，我们需要把负环中的点能到达其他点都标记为‘？’点，因为这些点在有限次循环后

会变成负值，一定小于3，可以用dfs来遍历能经过的所有点。

---

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

 typedef long long LL;
 #define inf 1e9
 #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 tot[N];
 bool vis[N];
 int tmp[N];
 bool bad[N];
 int dis[N];
 stack<int> sta;
 int cnt;
 int bus[N];
 int n,m;

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

 void add(int u,int v,int w){
     e[cnt].to = v;
     e[cnt].w = w;
     e[cnt].next = head[u];
     head[u] = cnt++;
 }
 //遍历所有能到达的点
 void dfs(int u){

     bad[u] = true;

     for(int o = head[u]; ~o; o = e[o].next){
         if(!bad[e[o].to])
             dfs(e[o].to);
     }
 }

 void SPFA(){

     while(!sta.empty()) sta.pop();
     rep(i,,n) vis[i] = false;
     rep(i,,n) bad[i] = false;
     rep(i,,n) dis[i] = inf;
     rep(i,,n) tot[i] = ;
     dis[] = ;
     sta.push();

     int u,v,w;
     while(!sta.empty()){
         u = sta.top();
         sta.pop();
         if(bad[u]) continue; //‘？’点
         vis[u] = false;

         for(int o = head[u]; ~o; o = e[o].next){
             w = e[o].w;
             v = e[o].to;

             if(!bad[v]/* '?'点 */ && dis[u] + w < dis[v]){
                 dis[v] = dis[u] + w;
                 // printf("this is dis[%d] = %d\n",v,dis[v]);
                 if(!vis[v]){
                     if(++tot[v] > n) dfs(v);
                     else{
                         vis[v] = true;
                         sta.push(v);
                     }
                 }
             }
         }
     }
 }

 void print(int o){

     int tot;
     scanf("%d",&tot);
     rep(i,,tot){
         scanf("%d",&tmp[i]);
     }
     printf("Case %d:\n",o);
     rep(i,,tot){
         if(bad[tmp[i]] || dis[tmp[i]] <  || dis[tmp[i]] == inf) printf("?\n");
         else printf("%d\n",dis[tmp[i]]);
     }
 }

 int main(){

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

     int u,v;
     rep(o,,T){
         scanf("%d",&n);
         rep(i,,n){
             scanf("%d",&bus[i]);
         }

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

         scanf("%d",&m);
         rep(i,,m){
             scanf("%d%d",&u,&v);
             add(u,v,(bus[v] - bus[u])*(bus[v] - bus[u])*(bus[v] - bus[u]));
         }

         SPFA();
         print(o);
     }

     getchar(); getchar();
     return ;
 }