LintCode 777. Valid Perfect Square

Posted 2020-10-22 zslhg903

Given a positive integer num, write a function which returns True if num is a perfect square else False.

 

样例

For example:
Given num = 16
Returns True

 

解法一：牛顿迭代器

class Solution {
public:
    /**
     * @param num: a positive integer
     * @return: if num is a perfect square else False
     */
    bool isPerfectSquare(int num) {
        // write your code here
        double pre=0,res=1;
        while(pre!=res)
        {
            pre=res;
            res=(res+num/res)/2;
        }
        int t=(int)res;
        return t*t==num;
    }
};

解法二：二分法

class Solution {
public:
    /**
     * @param num: a positive integer
     * @return: if num is a perfect square else False
     */
    bool isPerfectSquare(int num) {
        // write your code here
        long left=0,right=num,mid;
        while(left<=right)
        {
            mid=left+(right-left)/2;
            long res=mid*mid;
            if(res<num)
            {
                left=mid+1;
            }
            else if(res>num)
            {
                right=mid-1;
            }
            else
            {
                return true;
            }
        }
        return false;
    }
};