Leetcode 69 Sqrt(x)

 1 public int sqrt(int x) {
 2         long low = 0;
 3         long up = (long)x;
 4         while(low <= up){
 5             long mid = (low + up) / 2;
 6             if(mid * mid > x)
 7                 up = mid - 1;
 8             else if(mid * mid < x)
 9                 low = mid + 1;
10             else
11                 return (int)mid;
12         }
13         return (int)up;
14     }