MagicLen

use std::cmp::Ordering;

impl Solution {
    pub fn my_sqrt(x: i32) -> i32 {
        if x == 0 {
            return 0;
        }

        let mut s = 1;
        let mut e = x;

        while s <= e {
            let m = s + ((e - s) >> 1);

            // (m*m).cmp(&x)
            match m.cmp(&(x / m)) {
                Ordering::Equal => {
                    return m;
                }
                Ordering::Greater => {
                    e = m - 1;
                }
                Ordering::Less => {
                    s = m + 1;
                }
            }
        }

        e
    }
}