UVA 10986 Sending email 【dijkstra + 堆优化】

题目链接：
https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1927

题意：n个点m条边，求s到e的最短距离

代码：

#include<stdio.h>
#include<iostream>
#include<math.h>
#include<stdlib.h>
#include<ctype.h>
#include<algorithm>
#include<vector>
#include<string>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<string.h>

using namespace std;


const int INF = 0x3f3f3f3f;
const int MAXN = 1000010;

struct qnode
{
    int v;
    int c;
    qnode(int _v = 0, int _c = 0) :v(_v), c(_c){}
    bool operator < (const qnode &r) const
    {
        return c > r.c;
    }
};

struct Edge
{
    int v, cost;
    Edge(int _v = 0, int _cost = 0) :v(_v), cost(_cost) {}
};

vector<Edge> E[MAXN];
bool vis[MAXN];
int dist[MAXN];

void dijkstra(int n,int start,int ed)
{
    memset(vis, false, sizeof(vis));
    for (int i = 0; i < n; i++)
        dist[i] = INF;
    priority_queue<qnode> que;
    while (!que.empty()) que.pop();
    dist[start] = 0;
    que.push(qnode(start, 0));
    qnode tmp;
    while (!que.empty())
    {
        tmp = que.top(); que.pop();
        int u = tmp.v;
        if (vis[ed]) continue;
        if (vis[u]) continue;
        vis[u] = true;
        for (int i = 0; i < E[u].size(); i++)
        {
            int v = E[u][i].v;
            int cost = E[u][i].cost;
            if (!vis[v] && dist[v] > dist[u] + cost)
            {
                dist[v] = dist[u] + cost;
                que.push(qnode(v, dist[v]));
            }
        }
    }
}

void addedge(int u, int v, int w)
{
    E[u].push_back(Edge(v, w));
}

int n, m, s, d;
int a, b, c;

int main()
{
    int t;
    int cases = 1;
    scanf("%d",&t);
    while (t--)
    {
        scanf("%d%d%d%d", &n, &m, &s, &d);
        for (int i = 0; i <= n; i++) E[i].clear();
        while (m--)
        {
            scanf("%d%d%d", &a, &b, &c);
            addedge(a, b, c);
            addedge(b, a, c);
        }
        dijkstra(n, s, d);
        if (dist[d] == INF)
            printf("Case #%d: unreachable\n", cases++);
        else
            printf("Case #%d: %d\n", cases++, dist[d]);

    }
    return 0;
}