Lightoj1045——Digits of Factorial(k進位制的n的階乘位數)
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 |
結論:k進位制下的n的階乘的位數=logk(n)=log10(n)/(log10(k)),所以可以先求出10進位制下f[n]的對數打表。另外f[n]應先保持浮點型,最後向上取整
#include<stdio.h> #include<algorithm> #include<string.h> #include<iostream> #include<cmath> #define MAXN 1000010 using namespace std; double a[MAXN]; void Init() { a[0]=log10(1); for(int i=1;i<=1000000;++i) a[i]=a[i-1]+log10(i); } int main() { Init(); int ans; int t,cnt=1,i,j,m,n; scanf("%d",&t); while(t--) { scanf("%d%d",&n,&m); if(n==0) ans=1; else { ans=ceil(a[n]/log10(m)); } printf("Case %d: %d\n",cnt++,ans); } return 0; }