poj 3255

#include <bits/stdc++.h>

using namespace std;
#define INF 0x7ffffff
typedef pair<int, int> P;
#define maxn 100000+10

struct edge
{
    int to;
    int cost;
    edge(){}
    edge(int to_, int cost_)
    {
        to = to_;
        cost = cost_;
    }
};

int d[maxn], d2[maxn];
int N, R;
vector<edge> G[maxn];

void dijkstra(int s)
{
    priority_queue<P, vector<P>, greater<P> >que;
    fill(d, d+N, INF);
    fill(d2, d2+N, INF);
    d[s] = 0;
    que.push(P(0,s));
    while(!que.empty())
    {
        P p = que.top();
        que.pop();
        int v = p.second, dist = p.first;
        if(d2[v] < dist) continue;
        for(int i=0; i<G[v].size(); i++)
        {
            edge e = G[v][i];
            int a = dist + e.cost;
            if(d[e.to] > a)
            {
                swap(d[e.to] , a);
                que.push(P(d[e.to], e.to));
            }
            if(d2[e.to] > a && d[e.to] < a)
            {
                d2[e.to] = a;
                que.push(P(d2[e.to], e.to));
            }
        }
    }
}


int main()
{
    cin>>N>>R;
    int u, v, w;
    for(int i=0; i<R; i++)
    {
        cin>>u>>v>>w;
        G[u-1].push_back(edge(v-1, w));
        G[v-1].push_back(edge(u-1, w));
    }
     dijkstra(0);
     cout<<d2[N-1]<<endl;
    return 0;
}

poj 3255

原文：http://blog.csdn.net/dojintian/article/details/44725663