Sqrt(x)

class Solution {
    /**
     * @param x: An integer
     * @return: The sqrt of x
     */
    public int sqrt(int x) {
        // write your code here
        if (x < 0) {
            return -1;
        }
        
        if (x == 0 || x == 1) {
            return x;
        }
        
        long start = 1;
        long end = x;
        while (start + 1  < end) {
            long mid = start + (end - start) / 2;
            //System.out.println(start + " " + end + " "+ mid) ;
            if (mid * mid == x) {
                return (int)mid;
            } else if (mid * mid < x) {
                start = mid;
            } else {
                end = mid;
            }
        }
        
        if (start * start == x) {
            return (int)start;
        }
        
        if (end * end == x) {
            return (int)end;
        }
        
        if (end * end < x) {
            return (int)end;
        }
        
        return (int)start;
    }
}