hdu 4460

break point 在 边数很少，o(n*m)暴力出奇迹~~~

#include<iostream>
#include<map>
#include<string>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>

using namespace std;

const int maxn = 1005, maxm = 22222, inf=2000;
int n, m, cnt;
int h[maxn], d[maxn][maxn];
map<string, int> mp;

struct edge{
    int v, nxt;
}e[maxm];

void add(int u, int v){
    e[cnt] = (edge){v, h[u]};
    h[u]=cnt++;
    e[cnt]=(edge){u, h[v]};
    h[v]=cnt++;

    d[u][v]=d[v][u]=1;
}

int vis[maxn];
void dijkstra(const int s){
    queue<int> q;
    memset(vis, 0, sizeof(vis));
    q.push(s);  vis[s]=1;
    while(!q.empty()){
        int u = q.front(); q.pop();
        for(int i=h[u]; i!=-1; i=e[i].nxt){
            int v = e[i].v;
            if(vis[v]) continue;
            d[v][s]=d[s][v]=min(d[s][v], d[s][u]+1);
            q.push(v), vis[v]=1;
        }
    }
}

int main(){
    while(scanf(" %d", &n)==1 && n){
        int i, j;
        string s1, s2;
        char n1[12], n2[12];
        mp.clear();
        for(i=0; i<n; i++){
            scanf(" %s", n1);
            mp[s1=n1]=i;
        }
        cnt=0;
        memset(h, -1, sizeof(h));
        for(i=0; i<n; i++)
            for(j=0; j<n; j++)
                d[i][j]=i==j?0:inf;
        scanf(" %d", &m);
        while(m--){
            scanf(" %s %s", n1, n2);
            add(mp[s1=n1], mp[s2=n2]);
        }

        for(i=0; i<n; i++) dijkstra(i);

        int ans = 0;
        for(i=0; i<n; i++)
            for(j=i+1; j<n; j++){
                ans=max(ans, d[i][j]);
            }
        printf("%d
", ans==inf?-1:ans);
    }
    return 0;
}