【UvaOJ】【基础题目】【Maths - Misc】 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 integern 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

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解题思路：
觉得题目没什么意思，无非是公式推导，虽然开始我也没想出来怎么做。
要注意的一点是取对数方法能使运算简便：

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代码：

#include<iostream>
#include<fstream>
#include<vector>
#include<cmath>
using namespace std;

int main()
{
int y;
while (cin >> y)
{
if (y == 0)
break;
else
{
y = (y - 1960) / 10;
int bit = pow(2, y + 2);
//long long max = 0;
//for (int i = 0; i < bit; i++)
///	max += pow(2, i);
double count = 1.0;
double all = 0;
while (all <= bit*log(2))
{
all += log(count);
count = count + 1;
}
cout << count - 2 << endl;
}
}
}