sqrtx.cpp

// Time:  O(logn)
// Space: O(1)

class Solution {
public:
    int mySqrt(int x) {
        if (x < 2) {
            return x;
        }
        
        int left = 1, right = x / 2;
        while (left <= right) {
            const auto mid = left + (right - left) / 2;
            if (mid > x / mid) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }

        return left - 1;
    }
};