zoj 2818 Root of the Problem

Root of the Problem

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Time Limit: 2 Seconds      Memory Limit: 65536 KB

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Given positive integers B and N, find an integer A such that A^N is as close as possible to B. (The result A is an approximation to the Nth root of B.) Note that A^N may be less than, equal to, or greater than B.

Input: The input consists of one or more pairs of values for B and N. Each pair appears on a single line, delimited by a single space. A line specifying the value zero for both B and N marks the end of the input. The value of B will be in the range 1 to 1,000,000 (inclusive), and the value of N will be in the range 1 to 9 (inclusive).

Output: For each pair B and N in the input, output A as defined above on a line by itself.

#include <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;
int main(){
    double b, n;
    while(cin >> b >> n){
        if(b == 0 && n == 0)
            break;
        //pow:double pow(double, double)
        int a = (int)pow(b, 1/ n);//直接取整，不是四舍五入 ,pow(a, n) < b
        if(b - pow(a, n) < pow(a + 1, n) - b)
            cout << a << endl;
        else
            cout << a + 1 << endl;
    }
    return 0;
}

Example Input:	Example Output:
4 3 5 3 27 3 750 5 1000 5 2000 5 3000 5 1000000 5 0 0	1 2 3 4 4 4 5 16