B12 - Equation

atcoder.jp

1 ≦ N ≦ 100000 で、x * x * x + x = N になる x を探すわけだから、x が 100 未満なのは確実。

var N = int.Parse(Console.ReadLine()!);

var left = 0.0;
var right = 100.0;
while ((right - left) >= 0.001)
{
    var x = (left + right) / 2.0;
    var a = f(x);
    if (a <= N)
    {
        left = x;
    }
    else
    {
        right = x;
    }
}

Console.WriteLine(left);

double f(double x) => x * x * x + x;