lintcode-x的平方根-141

class Solution {
public:

    int sqrt(int x) {
        int left = 0, right = x/2;  
        long long mid = 0;  
        while (left <= right) {  
            mid = (right+left)/2;  
            long long cur = mid*mid;  
            long long pre = (mid+1)*(mid+1);
            
            if(cur==x)
                return mid;
            else if(x<pre&&x>cur)
                return mid;
            else if(cur>x)
                right=mid-1;
            else
                left=mid+1;
           
        }  
        return 1;  
    }
};