LightOJ1104-Birthday Paradox

Birthday Paradox

 

题意：假设一年有n天，现在你要邀请一些人来party，那么至少邀请几个人,可以保证party中至少两个人同一天生日的概率大于等于0.5？

解题思路：转化一下题意，求所有人生日都不同的概率小于等于0.5(那么至少两个人同一天就是大于等于0,5)

#include <iostream>#include <cstdio>#include <string>#include <cstring>#include <algorithm>#include <queue>#include <cmath>#include <vector>#include <set>#include <bitset>#include <stack>#include <map>#include <climits>#include <functional>using namespace std;#define LL long longconst int INF=0x3f3f3f3f;const double eps=1e-8;int main(){    int t,n;    int cas=1;    scanf("%d",&t);    while(t--)    {        scanf("%d",&n);        double ans=1;        int i;        for(i=n-1;i>=1;i--)        {            ans*=1.0*i/ n;            if(ans<=0.5) break;        }        printf("Case %d: %d\n",cas++,n-i);    }    return 0;}