hdu1595find the longest of the shortest 最短路

//给一个无向图，问删除一条边，使得从1到n的最短路最长
//问这个最长路
//这个删除的边必然在最短路上，如果不在，那么走这条最短路肯定比其他短
//枚举删除这条最短路的边，找其最长的即为答案
#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std ;
const int maxn = 1110 ;
const int inf = 0x3f3f3f3f;
struct Edge
{
    int u , v , w ;
    int next ;
}edge[maxn*maxn] ;
int head[maxn] ;
int nedge ;
int F[maxn] ;
int vis[maxn] ;
int dis[maxn] ;
int a[maxn] ;
int n , m;
void addedge(int u , int v , int w)
{
    edge[nedge].u = u ;
    edge[nedge].v = v ;
    edge[nedge].w = w ;
    edge[nedge].next = head[u] ;
    head[u] = nedge++ ;
}

void dijkstra(int num)
{
    memset(vis , 0 , sizeof(vis)) ;
    for(int j = 2;j <= n;j++)
    dis[j] = inf ;
    dis[1] = 0 ;
    while(1)
    {
        int mi = inf; int pos ;
        for(int j = 1 ;j <= n;j++)
        if(!vis[j] && dis[j] < mi)
        mi = dis[pos = j] ;
        if(mi == inf)break;
        vis[pos] = 1 ;
        for(int i = head[pos] ;i != -1 ;i = edge[i].next)
        {
            if(i == num || i == (num^1))
            continue ;
            int v = edge[i].v;
            if(dis[v] > dis[pos] + edge[i].w)
            {
                dis[v] = dis[pos] + edge[i].w ;
                F[v] = i ;
            }
        }
    }
}
int main()
{
    //freopen("in.txt" ,"r" , stdin) ;
    while(~scanf("%d%d" , &n , &m))
    {
        memset(head , -1 , sizeof(head)) ;
        nedge = 0 ;
        memset(F , 0 , sizeof(F)) ;
        while(m--)
        {
            int u , v , w ;
            scanf("%d%d%d" ,&u , &v ,&w) ;
            addedge(u , v , w) ;
            addedge(v , u , w) ;
        }
        dijkstra(nedge) ;
        int u = n ;
        int ans = 0 ;
        int len = 0 ;
        while(1)
        {
            if(u == 1)break ;
            a[++len] = F[u] ;
            u = edge[F[u]].u ;
        }
        for(int i = 1;i <= len;i++)
        {
            dijkstra(a[i]) ;
            ans = max(ans , dis[n]) ;
        }
        cout<<ans<<endl;
    }
    return  0 ;
}