题目描述

此处只需要注意一点，就是三次方存在复数，对于复数情况下，l = input, r = 0

算法1

(二分) $O(logn)$

C++ 代码

#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

int main()
{
    double input;
    cin >> input;

    double l, r;

    if(input >= 0) l = 0, r = input;
    else l = input, r = 0;
    while(fabs(l - r) > 1e-8)
    {
        double mid = (l + r) / 2;
        if(mid * mid * mid >= input) r = mid;
        else l = mid;
    }

    printf("%.6f\n", l);
    return 0;
}