LintCode 141---x的平方根

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