【ATT】【second】Sqrt(x)

二分查找。要注意越界问题。以及除数是否为0的情况

    int sqrt(int x) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(x<=1)
            return x;
        int left = 1,right = x;
        while(left<=right)
        {
            int mid = left + (right-left)/2;
            int tmp = x/mid;  //用除法，因为mid*mid可能越界；用除法的话，考虑分母是否为0，因此x从2开始计算，那么mid不可能为0
            if(tmp<mid)
                right = mid-1;
            else if(tmp>mid)
                left = mid+1;
            else
                return mid;
        }
        return right; //返回的是right
    }