[lintcode easy]Sqrt(x)

Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

 

Example

sqrt(3) = 1

sqrt(4) = 2

sqrt(5) = 2

sqrt(10) = 3

Challenge

O(log(x))

直接的做法是

注意不要直接判断i*i  会overflow

class Solution {
    /**
     * @param x: An integer
     * @return: The sqrt of x
     */
    public int sqrt(int x) {
        // write your code here
        
        if(x<=1) return x;
        int i=0;
        
        for(i=1;i<=x;i++)
        {
          
            if(i<=x/i && i+1>x/(i+1))
            {
               break;
                
            }
        }
        
     return i;
    }
}

 

 

使用二分查找的做法。

 

class Solution {
    /**
     * @param x: An integer
     * @return: The sqrt of x
     */
    public int sqrt(int x) {
        // write your code here
        
        if(x<=1) return x;
        int i=0;
        
        int beg=1;
        int end=x;
        
        int mid=0;
        
        while(beg<end)
        {
            mid=(end+beg)/2;
            
            if(x/mid==mid)
            {
                return mid;
            }
            else
            {
                if(mid<x/mid)
                {
                    beg=mid+1;
                }
                else
                {
                    end=mid-1;
                }
            }
        }
        
        return end;
    }
}