[Leetcode 69, Medium] Sqrt(x)

int sqrt(int x)

int mySqrt(int x) {
        if(x < 0)
            return -1;
        if(x <= 1)
            return x;

        unsigned long long start = 1;
        unsigned long long end = x / 2 + 1;
        while(start <= end) {
            unsigned long long mid = (start + end) / 2;
            unsigned long long square = mid * mid;
            if(x == square)
                return mid;
            else if(x > square)
                start = mid + 1;
            else
                end = mid - 1;
        }
        
        return end;
    }