Light OJ 1045 Digits of Factorial（求位數）

1045 - Digits of Factorial

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Time Limit: 2 second(s)

Memory Limit: 32 MB

Factorial of an integer is defined by the following function

f(0) = 1

f(n) = f(n - 1) * n, if(n > 0)

So, factorial of 5 is 120. But in different bases, the factorial may be different. For example, factorial of 5 in base 8 is 170.

In this problem, you have to find the number of digit(s) of the factorial of an integer in a certain base.

Input

Input starts with an integer T (≤ 50000), denoting the number of test cases.

Each case begins with two integers n (0 ≤ n ≤ 10⁶) and base (2 ≤ base ≤ 1000). Both of these integers will be given in decimal.

Output

For each case of input you have to print the case number and the digit(s) of factorial n in the given base.

Sample Input	Output for Sample Input
5 5 10 8 10 22 3 1000000 2 0 100	Case 1: 3 Case 2: 5 Case 3: 45 Case 4: 18488885 Case 5: 1

 

與白書裏面推薦的一道UVA題目很像，http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1002

也是利用對數來求位數。

代碼：

#include<stdio.h>
#include<cmath>
using namespace std;
double a[1000010];
int main()
{
  freopen("in.txt","r",stdin);
  a[1]=log(1);
  for(int i=2;i<=1000000;i++)a[i]=a[i-1]+log(i);
  int t;
  scanf("%d",&t);
  for(int ca=1;ca<=t;ca++)
  {
    int n,b;
    scanf("%d%d",&n,&b);
    if(n==0)
    {
      printf("Case %d: %d\n",ca,1);
      continue;
    }
    double ans=0;
    printf("Case %d: %.0lf\n",ca,floor(a[n]/log(b*1.0))+1);
  }
  return 0;
}