SOJ 1017 Power of Cryptography 库函数精度

Posted 2020-10-09 87hbteo

Background

Current work in cryptography involves (among other things) large prime numbers and computing powers of numbers modulo functions of these primes. Work in this area has resulted in the practical use of results from number theory and other branches of mathematics once considered to be of only theoretical interest.

This problem involves the efficient computation of integer roots of numbers.

 

The Problem

Given an integer  and an integer  you are to write a program that determines  , the positive  root of p. In this problem, given such integers n and p, p will always be of the form  for an integer k (this integer is what your program must find).

 

The Input

The input consists of a sequence of integer pairs n and p with each integer on a line by itself. For all such pairs  ,  and there exists an integer k,  such that  .

 

The Output

For each integer pair n and p the value  should be printed, i.e., the number k such that  .

 

Sample Input

 

2
16
3
27
7
4357186184021382204544

 

Sample Output

 

4
3
1234

解题思路：
　　本题直接用pow求解就好，不过可能存在四舍五入一类的精度问题需要处理，所以要特别小心
AC代码：

#include<stdio.h>
#include<math.h>
int main()
{
    double p,k;
    double n;
    while(scanf("%lf%lf",&n,&p)==2)
    {
        k=  pow (p,1.0/n);
        long long ans=k;
        if(pow(ans,n)!=p)printf("%ld\n",ans+1);
        else printf("%ld\n",ans);
    }
    return 0;
}