ZOJ 3696 Alien's Organ(泊松分布)

题目链接：ZOJ 3696 Alien's Organ

满足泊(bo)松分布，用公式计算一下和就行了，注意求阶乘那里要用double，否则会溢出。

#include <iostream>#include <cstdio>#include <cmath>using namespace std;int n;double q;double f(int k){    if(k == 0)        return 1;    return k * f(k - 1);}double getP(int k){    return pow(q, k) * exp(-q) / f(k);}int main(){    int T;    scanf("%d", &T);    while(T--)    {        scanf("%d%lf", &n, &q);        double sum = 0.0;        for(int i = 0; i <= n; i++)            sum += getP(i);        printf("%.3lf\n", sum);    }    return 0;}