UVA 10986 Sending email 最短路问题

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <stack>
#include <queue>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
#define LL long long
#define PI 3.1415926535897932626
using namespace std;
int gcd(int a, int b) {return a % b == 0 ? b : gcd(b, a % b);}
int N,M,S,T;
const int INF = 0x3f3f3f3f;
typedef pair<int,int> pii;
#define MAXN 20005
priority_queue<pii,vector<pii>,greater<pii> >q;
struct node
{
    int v;
    int w;
};
vector <node>G[MAXN];//G[u].v = w present dis[u][v] = w;
int d[MAXN];
void read()
{
    scanf("%d%d%d%d",&N,&M,&S,&T);
    for (int i = 0; i <= N; i++)G[i].clear();
    while (M--)
    {
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        node tmp; tmp.v = v; tmp.w = w;
        G[u].push_back(tmp);
        tmp.v = u; tmp.w = w;
        G[v].push_back(tmp);
    }
}
void dijkstra(int st)
{
    memset(d,0x3f,sizeof(d));
    d[st] = 0;
   // printf("%d\n",st);
    while (!q.empty()) q.pop();
    q.push(make_pair(d[st],st));
    while (!q.empty())
    {
        pii u = q.top(); q.pop();
        int x = u.second;
        if (u.first != d[x]) continue;
        for (int i = 0; i < (int)G[x].size(); i++)
        {
            int v = G[x][i].v, w = G[x][i].w;
            //printf("%d %d\n",v,w);
            if (d[v] > d[x] + w)
            {
                d[v] = d[x] + w;
                //printf("%d %d\n",d[v],v);
                q.push(make_pair(d[v],v));
            }
        }
    }
}
int main()
{
    int num, kase = 1;
    scanf("%d",&num);
    while (num--)
    {
        read();
        dijkstra(S);
        if (d[T] == INF) printf("Case #%d: unreachable\n",kase++);
        else printf("Case #%d: %d\n",kase++,d[T]);
    }
    return 0;
}