題目：hdu4460

題意：尋找每兩點之間最短路中的最長路。若存在某兩點不連通，就輸出-1.

解答：對每個點spfa，然後找最長的邊。用鄰接連結串列存~~注意：雙向邊！

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<queue>
#include<algorithm>
#include<map>
using namespace std;
const int MAXN = 10010 + 10010;
const int INF = 1 << 30;
int w[MAXN],u[MAXN],v[MAXN];
int first[1100],Next[MAXN],dis[1100];
int book[1100];
int ans;
int n,m;
queue<int> q;
int spfa(int a)
{
    int Max = 0;
    while(!q.empty())
        q.pop();
//    for(int i = 0;i < n;i++)
//        first[i] = -1;
    for(int i = 0;i < n;i++)
        book[i] = 0;
    for(int i = 0;i < n;i++)
        dis[i] = INF;
    dis[a] = 0;
    q.push(a);
    book[a] = 1;
    while(!q.empty())
    {
        int k = first[q.front()];
        while(k!=-1)
        {
            if(dis[v[k]] > dis[u[k]] + w[k])
            {
                dis[v[k]] = dis[u[k]] + w[k];
                if(book[v[k]] == 0)
                {
                    q.push(v[k]);
                    book[v[k]] = 1;
                }
            }
            k = Next[k];
        }
        book[q.front()] = 0;
        q.pop();
    }
    return 0;
}
int main()
{
    map<string,int> M;
    char tmp[12],tmp1[12],tmp2[12];
    while(scanf("%d",&n))
    {
        if(n == 0)
            break;
        int tot = 0;
        for(int i = 0;i < n;i++)
        {
            scanf("%s",tmp);
            M[tmp] = tot++;
        }
        for(int i = 0;i < n;i++)
            first[i] = -1;
        scanf("%d",&m);
        for(int i = 0;i < 2*m;i+=2)
        {
            scanf("%s%s",tmp1,tmp2);
            u[i] = M[tmp1];
            v[i] = M[tmp2];
            Next[i] = first[u[i]];
            first[u[i]] = i;
            w[i] = 1;
            u[i+1] = M[tmp2];
            v[i+1] = M[tmp1];
            Next[i+1] = first[u[i+1]];
            first[u[i+1]] = i+1;
            w[i+1] = 1;
        }
        m = m * 2;
        int result = 0;
        for(int i = 0;i < n;i++)
        {
            spfa(i);
            int ok = 1;
            for(int j = 0;j < n;j++)
            {
                if(dis[j]  == INF)
                    {
                        int ok = 0;
                        result = -1;
                        break;
                    }
                result = max(result,dis[j]);
            }
            if(ok == 0)
                break;
        }
        printf("%d\n",result);
    }
    return 0;
}