UVA821 PageHopping （Floyd）

求所有点直接的平均最短距离，保存一下出现过的点，题目保证是所有点连通，Floyd求出最短路以后两个for统计一下。

#include<bits/stdc++.h>
using namespace std;

const int maxn = ;

int g[maxn][maxn];
bool vis[maxn];
vector<int> p;
const int INF = 0x3f3f3f3f;

int main()
{
    //freopen("in.txt","r",stdin);
    int u,v,kas = ;
    memset(g,0x3f,sizeof(g));
    for(int i = ; i < maxn; i++) g[i][i] = ;
    while(scanf("%d%d",&u,&v),u){
        p.clear(); memset(vis,,sizeof(vis));
        g[u][v] = ; vis[u] = vis[v] = true;
        while(scanf("%d%d",&u,&v),u){
            g[u][v] = ;
            vis[u] = vis[v] = true;
        }
        for(int i = ; i < maxn; i++){
            if(vis[i]) p.push_back(i);
        }
        int sz = p.size();

        for(int k = ; k < sz; k++){
            int m = p[k];
            for(int i = ; i < sz; i++){
                int u = p[i];
                if(g[u][m]<INF){
                     for(int j = ; j < sz; j++){
                        int v = p[j];
                        g[u][v] = min(g[u][v],g[u][m]+g[m][v]);
                    }
                }
            }
        }

        int sum = ;
        for(int i = ; i < sz; i++){
            int u = p[i];
            for(int j = ; j < sz; j++) if(i!=j){
                int v = p[j];
                sum += g[u][v];
                g[u][v] = INF;
            }
        }
        printf("Case %d: average length between pages = %.3lf clicks\n",++kas,(double)sum/(sz*(sz-)));
    }
    return ;
}