LeetCode 69: Sqrt(x)

class Solution {
    public int mySqrt(int x) {
        if (x < 0) {
            return -1;
        }
        
        if (x < 2) {
            return x;
        }
        int start = 1;
        int end = x;
        while (end - start > 1) {
            int mid = start + (end - start)/2;
            if (mid == x / mid) {
                return mid;
            } else if (mid > x / mid) {
                end = mid;
            } else {
                start = mid;
            }
        }
        return start;
    }
}