Poj 1511 invitation cards (spfa)

A group of students send invitations to each station in the city. Each station has exactly one student. There is a specific fare between any two stations. If the students depart from station 1 in the morning and return to station 1 in the evening, the minimum cost is required.
Question: The first spfa in life. The question is clear, and the shortest path with permission is obtained. Create a reverse graph when you return.

#include <queue>#include <iostream>using namespace std;#define N 1000001#define INF 1999999999struct Edge{int v, w, next;} edgeGo[N], edgeBack[N];int P, Q;int dis[N];int headGo[N], headBack[N];bool mark[N];queue<int>que;void spfa ( Edge edge[], int head[] ){memset(mark,0,sizeof(mark));while ( ! que.empty() ) que.pop();int i, u, v;for ( i = 1; i <= P; i++ )dis[i] = INF;dis[1] = 0;mark[1] = 1;que.push(1);while ( !que.empty () ){u = que.front();que.pop();mark[u] = 0;for ( i = head[u]; i != 0; i = edge[i].next ){v = edge[i].v;if ( dis[v] > dis[u] + edge[i].w ){dis[v] = dis[u] + edge[i].w;if ( ! mark[v] ){que.push ( v );mark[v] = 1;}}}}}int main(){int t, k, u, v, w;scanf("%d",&t);while ( t-- ){k = 0;memset(headGo,0,sizeof(headGo));memset(headBack,0,sizeof(headBack));scanf("%d%d",&P,&Q);while ( Q-- ){scanf("%d%d%d",&u,&v,&w);k++;edgeGo[k].v = v;edgeGo[k].w = w;edgeGo[k].next = headGo[u];headGo[u] = k;edgeBack[k].v = u;edgeBack[k].w = w;edgeBack[k].next = headBack[v];headBack[v] = k;}int i;    __int64 ans = 0;spfa ( edgeGo, headGo );for ( i = 1; i <= P; i++ )ans += dis[i];spfa ( edgeBack, headBack );for ( i = 1; i <= P; i++ )ans += dis[i];printf("%I64d\n",ans);}return 0;}