水题， Floyd一遍就完了。
#include<cstdio>
#include<algorithm>
#define REP(i, a, b) for(int i = (a); i < (b); i++)
using namespace std;const int MAXN = 101;
int d[MAXN][MAXN], n;int main()
{int u, v, kase = 0;while(~scanf("%d%d", &u, &v) && u && v){REP(i, 1, MAXN)REP(j, 1, MAXN)d[i][j] = (i == j ? 0 : 1e9);while(1){d[u][v] = 1;if(!(~scanf("%d%d", &u, &v) && u && v)) break;}REP(k, 1, MAXN)REP(i, 1, MAXN)REP(j, 1, MAXN)d[i][j] = min(d[i][j], d[i][k] + d[k][j]);int sum = 0, cnt = 0;REP(i, 1, MAXN)REP(j, 1, MAXN)if(d[i][j] != 1e9 && i != j){cnt++;sum += d[i][j];}printf("Case %d: average length between pages = %.3f clicks\n", ++kase, (double)sum / cnt);}return 0;
}