Factstone Benchmark

Factstone Benchmark

时间： 1ms        内存：128M

描述：

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.

 

输入：

输出：

示例输入：

1960
1981
0

示例输出：

3
8

提示：

参考答案（内存最优[980]）：

#include<stdio.h>
#include<math.h>
int main()
{
	int y,i;
	double sum;
	while(scanf("%d",&y)!=EOF,y)
	{
		sum=0;
		if(y==1960)
			printf("3\n");
		else
		{
			for(i=1;;i++)
			{
				sum+=log10(i)/log10(2);
				if(sum>pow(2,(y-1960)/10+2))
					break;
			}
			printf("%d\n",i-1);
		}
	}
	return 0;
}

参考答案（时间最优[64]）：

#include <iostream>
#include <cmath>
#define MAX 21
using namespace std;
int f[MAX];
int g[MAX];
int main()
{
    int i;
    f[0]=1<<2;
    g[0]=3;
    for(i=1;i<MAX;i++)
    {
        f[i]=f[i-1]<<1;
        int m=f[i];
        double sum=0;
        int base=2;
        while(sum+log2(base)<=m)
        {
            sum+=log2(base);
            base++;
        }
        g[i]=base-1;
    }
    int n;
    while(cin>>n&&n)
    {
        int t=(n-1960)/10;
        cout<<g[t]<<endl;
    }
    return 0;
}

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