UVA10392 Factoring Large Numbers

思路：质因分解..

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
#define LL long long
int main()
{
    LL num;
    while(cin>>num)
	{
        if(num < 0)    
			break;
        for(LL i = 2; i <= (int)sqrt(num); i++)
            while(num % i == 0)
			{
                cout<<"    ";
                cout<<i<<endl;
                num /= i;
            }
        if(num > 1) cout<<"    "<<num<<endl;
        cout<<endl;
    }
}

One of the central ideas behind much cryptography is that factoring large numbers is computationally

intensive. In this context one might use a 100 digit number that was a product of two 50 digit prime

numbers. Even with the fastest projected computers this factorization will take hundreds of years.

You don’t have those computers available, but if you are clever you can still factor fairly large

numbers.

Input

The input will be a sequence of integer values, one per line, terminated by a negative number. The

numbers will fit in gcc’s long long int datatype, however scanf and printf do not appear to handle

this datatype correctly, so you must do your own I/O conversion.

Output

Each positive number from the input must be factored and all factors (other than 1) printed out. The

factors must be printed in ascending order with 4 leading spaces preceding a left justified number, and

followed by a single blank line.

Sample Input

90

1234567891

18991325453139

12745267386521023

-1

Sample Output

2

3

3

5

1234567891

3

3

13

179

271

1381

2423
30971
411522630413