hdu1018 Big Number (阶乘的位数)

Big Number

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 14952 Accepted Submission(s): 6631


[align=left]Problem Description[/align]

In many applications very large integers numbers are required. Some of these applications are using keys for secure transmission of data, encryption, etc. In this problem you are given a number, you have to determine the number of digits in the factorial of the number.

[align=left]Input[/align]

Input consists of several lines of integer numbers. The first line contains an integer n, which is the number of cases to be tested, followed by n lines, one integer 1 ≤ n ≤ 107 on each line.

[align=left]Output[/align]

The output contains the number of digits in the factorial of the integers appearing in the input.

[align=left]Sample Input[/align]

2
10
20

[align=left]Sample Output[/align]

7
19

题意：给你一个 n ，计算 n！ 有多少位数
分析：
123456=1.23456*10^5;
log10(123456)=5.09151;
log10(1.23456*10^5)=log10(1.23456)+log10(10^5)=0.09151+5;
故int(log10(n))+1 就是n的位数

View Code

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
int n,test,i,ans;
double t;
cin>>test;
while(test--)
{
cin>>n;
t=0;
for(i=2;i<=n;i++)
t+=log10(i*1.0);
ans=int(t)+1;
cout<<ans<<endl;
}
return 0;
}