uva 10916 - Factstone Benchmark
Problem B: Factstone Benchmark
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
1960 1981 0
Output for Sample Input
3 8
计算 n的最大值，2^n>n!，以前做过的题开始有傻乎乎的直接算忘记n！很大会越界，取对数可以解决
lg（2^n）>lg（n！）
n*lg2>lg1+.......lgn
#include<stdio.h>
#include<math.h>
void main()
{int n,i;
double m,s;
while (scanf("%d",&n),n)
{m=pow(2,(n-1940)/10)*log(2);
s=0;
for (i=1;s<m;i++)
s+=log(i);
printf("%d\n",i-2);
}
}