华为机试：求解立方根

#include <iostream>
#include <algorithm>
#include <iomanip>
using namespace std;

double binarysearch(double val) {
    double r = val > 1 ? val : 1;
    double l = val < 1 ? val : 1;
    double mid;
    while (r - l > 0.001) {
        mid = (r + l) / 2;
        if (mid * mid * mid < val) {
            l = mid;
        }
        else {
            r = mid;
        }
    }
    return mid;
}

int main() {
    double val;
    cin >> val;
    if (val < 0) {
        cout << '-';
        val = -val;
    }
    cout << fixed << setprecision(1) << binarysearch(val) << endl;
    return 0;
}