zoj 3551 Bloodsucker

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int N = 100010;double dp[N], p;int T, n;int main(){ scanf("%d", &T); while(T--) { scanf("%d%lf", &n, &p); dp[n] = 0; for(int i = n - 1; i; --i) { double p0 = p * i * (n - i) * 2 / n / (n - 1); dp[i] = dp[i + 1] + 1 / p0; } printf("%.3lfn", dp[1]); } return 0;}