uva 113 - Power of Cryptography

Power of Cryptography

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

感觉double会有精度问题还是水过了。。

#include<stdio.h>

#include<math.h>

void main()

{double n,p;

long left,right,mid;

while (scanf("%lf%lf",&n,&p)!=EOF)

{left=0; right=1000000000;

while (left<right)

{mid=(left+right)/2;

if (pow(mid,n)==p) break;

if (pow(mid,n)>p) right=mid;

if (pow(mid,n)<p) left=mid;

}

printf("%d\n",mid);

}

}