【Leetcode】Sqrt(x)

题目链接：https://leetcode.com/problems/sqrtx/
题目：

Implement int sqrt(int x).

Compute and return the square root of x.

思路：

 二分法搜索平方数 要注意，如果不能完整的开方，要取靠左边的数，

算法：

public int mySqrt(int x) {  
    int left = 1,right = x,mid =0;  
    int last_mid = mid;  
    while(left<=right){  
        mid = left+(right-left)/2;  
          
        if(mid>x/mid){  
            right = mid-1;  
        }else if(mid<x/mid){  
            left = mid+1;  
            last_mid = mid;  
        }else{  
            return mid;  
        }  
    }  
    return last_mid;  
}