康康的阶乘

1760: 康康的阶乘

时间限制: 1 Sec  内存限制: 128 MB
提交: 223  解决: 44
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题目描述

 

In class, kangkang learned to use the computer to solve N factorial, and then came home to show off to Jane. In order not to let kangkang be too complacent, Jane gave kangkang a question "since you're going to ask for N factorial, you'll help me figure out 1! + 2! -3! + 4! -5! +... N!" It is. Can you help him?

 

输入

The first line enters an integer T (0 < = 20), which represents T group test data.

After that, it has T rows, and each row enters a positive integer N (0 < N < = 20).

输出

Each group of test data accounts for one line, output 1! + 2! - 3! +... .. N! The value of the.

样例输入

2
4

样例输出

3
21

---

---

#include<stdio.h>
int main() {
 long long a[30];//用long long。
 a[0]=1;
 for(int i=1; i<=20; i++)
  a[i]=a[i-1]*i;
 预处理，防止超时。
 int t,n;
 long long ans;
 scanf("%d",&t);
 while(t--) {
  ans=1;
  scanf("%d",&n);
  if(n==1)
   printf("1\n");
  else {
   for(int i=2; i<=n; i++) {
    if(i%2==0)
     ans+=a[i];
    else if(i%2==1)
     ans-=a[i];
   }
   printf("%lld\n",ans);
  }
 }
 return 0;
}