9. Palindrome Number

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本文介绍了一种在不使用额外空间的情况下判断整数是否为回文的方法。通过三种不同的Python实现方式，展示了如何高效地解决这个问题，并分析了每种方法的时间效率。

9. Palindrome Number

Leetcode link for this question

Discription:

Determine whether an integer is a palindrome. Do this without extra space.

click to show spoilers.

Some hints:
Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem “Reverse Integer”, you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

Analyze:

Code 1:

class Solution(object):
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        if x<0:
            return False
        for i in range(len(str(x))):
            if str(x)[i]==str(x)[len(str(x))-i-1]:
                continue
            else:
                return False
        return True

Submission Result:

Status: Accepted
Runtime: 392 ms
Ranking: beats 4.18%

Code 2:

class Solution(object):
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        if x<0:
            return False        
        st=str(x)
        le=len(st)
        for i in range(le):
            if st[i]==st[le-i-1]:
                continue
            else:
                return False
        return True

Submission Result:

Status: Accepted
Runtime: 292 ms
Ranking: beats 50.4%

Code 3:

class Solution(object):
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        if x<0:
            return False

        st=str(x)
        le=len(st)
        for i in range(le/2+1):
            if st[i]==st[le-i-1]:
                continue
            else:
                return False
        return True