POJ 3268 Silver Cow Party 最短路径 Dijkstra算法优化

堆优化的Dijkstra算法确实非常快，求解最短路径比BellmanFord算法和Floyd算法快了太多。

#include 
#include 
#include 
using namespace std;
typedef pair P;
vector
 edges[1007];
int d[1007], inf = 1000000000, N, M, X, fromEnd[1007];
bool used[1007];
void input()
{
    scanf("%d%d%d", &N, &M, &X);
    int from, to, cost;
    for (int i = 1; i <= M; i++)
    {
        scanf("%d%d%d", &from, &to, &cost);
        edges[from].push_back(P(cost, to));
    }
}
void dijkstra(int s)
{
    for (int i = 1; i <= N; i++)
    {
        d[i] = inf;
        used[i] = false;
    }
    d[s] = 0;
    priority_queue, greater
> que;
    que.push(P(0, s));
    while (!que.empty())
    {
        P current = que.top();
        que.pop();
        if (used[current.second] || current.first > d[current.second])
        {
            continue;
        }
        used[current.second] = true;
        for (int i = 0; i < edges[current.second].size(); i++)
        {
            P toEdge = edges[current.second][i];
            if (!used[toEdge.second] && d[current.second] + toEdge.first < d[toEdge.second])
            {
                d[toEdge.second] = d[current.second] + toEdge.first;
                que.push(P(d[toEdge.second], toEdge.second));
            }
        }
    }
}
void solve()
{
    dijkstra(X);
    for (int i = 1; i <= N; i++)
    {
        fromEnd[i] = d[i];
    }
    int ans = 0;
    for (int i = 1; i <= N; i++)
    {
        if (i == X)
        {
            continue;
        }
        dijkstra(i);
        if (fromEnd[i] + d[X] > ans)
        {
            ans = fromEnd[i] + d[X];
        }
    }
    printf("%d\n", ans);
}
int main()
{
    input();
    solve();
    return 0;
}