Square Root by binary search

Question

from lintcode
Find the square root of a number(integer).

Idea

Start from 0 to the given number. Perform a binary search to find a number whose square is closest but no larger than the given number.

public class Solution {
    /**
     * @param x: An integer
     * @return: The sqrt of x
     */
    public int sqrt(int x) {
        
        if (x == 0) return x;
        
        long start = 1;
        long end = x;
        while (start + 1 < end) {
            long mid = start + (end - start) / 2;
            if (mid * mid > x) {
                end = mid;
            } else {
                start = mid;
            }
        }
        if (start * start <= x)
          return (int)start;
        return (int)end;
    }
}