POJ 3255

题意： 次短路，

裸的板子；

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<map>
#include<set>
#include<vector>
#include<queue>
#include<stack>
using namespace std;
const int maxn = 1e5 +131;
const int INF = 0x7fffffff;
struct Edge{
    int to, cost;
    Edge(int a, int b) : to(a), cost(b) {}
};

vector<Edge> G[maxn];
void AddEdge(int from, int to, int cost) {
    G[from].push_back(Edge(to, cost));
    G[to].push_back(Edge(from, cost));
}

typedef pair<int, int> P;
int N, R;
int Dist[maxn], Dist2[maxn];

int Solve()
{
    priority_queue<P, vector<P>, greater<P> > que;
    fill(Dist, Dist + N, INF);
    fill(Dist2, Dist2 + N, INF);
    Dist[0] = 0;
    que.push(P(0,0));

    while(!que.empty())
    {
        P tmp = que.top(); que.pop();
        int v = tmp.second, d = tmp.first;
        if(Dist2[v] < d) continue;
        for(int i = 0; i < G[v].size(); ++i)
        {
            Edge &e = G[v][i];
            int d2 = d + e.cost;
            if(Dist[e.to] > d2) {
                swap(Dist[e.to], d2);
                que.push(P(Dist[e.to], e.to));
            }
            if(Dist2[e.to] > d2 && Dist[e.to] < d2)
            {
                Dist2[e.to] = d2;
                que.push(P(Dist2[e.to], e.to));
            }
        }
    }
    return Dist2[N-1];
}

int main()
{
    while(scanf("%d%d", &N, &R)!=EOF)
    {
        if(N == 0 && R == 0) break;
        for(int i = 0; i <= N; ++i) G[i].clear();
        for(int i = 0; i < R; ++i)
        {
            int u, v, c;
            scanf("%d%d%d", &u, &v, &c);
            AddEdge(u-1,v-1,c);
        }
        printf("%d\n",Solve());
    }
    return 0;
}