hduoj1141

Factstone Benchmark

Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 2101    Accepted Submission(s): 1179

Problem Description

Amtel has announced that it will release a 128-bit computer chip by 2010, a 256-bit computer by 2020, and so on, continuing its strategy of doubling the word-size every ten years. (Amtel released a 64-bit computer in 2000, a 32-bit computer in 1990, a 16-bit computer in 1980, an 8-bit computer in 1970, and a 4-bit computer, its first, in 1960.)
Amtel will use a new benchmark - the Factstone - to advertise the vastly improved capacity of its new chips. The Factstone rating is defined to be the largest integer n such that n! can be represented as an unsigned integer in a computer word.

Given a year 1960 ≤ y ≤ 2160, what will be the Factstone rating of Amtel's most recently released chip?

There are several test cases. For each test case, there is one line of input containing y. A line containing 0 follows the last test case. For each test case, output a line giving the Factstone rating.

 

Sample Input

196019810

 

Sample Output

38

题解：求出n!>2^bit的n取值。由于涉及到阶乘和幂，很容易超出LL的范围引发错误。所以考虑使用对数进行比较。即：log(n++)<bit*log(2);

代码：

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
int main()
{
 int n;
 while(cin >> n&&n)
 {
  int ans = 2;
  int cnt = (n-1960)/10+2;
  cnt = 1<<cnt;
  double s=0.0;
  while(s < cnt)
  {
   s+=log(ans)/log(2.0);
   ans++;
  }
  cout << ans-2 << endl;
 }
 return 0;
 }