LeetCode 009 Palindrome Number

LeetCode

Given an integer x, return true if x is palindrome integer.

An integer is a palindrome when it reads the same backward as forward.

For example, 121 is a palindrome while 123 is not.

Example 1:

Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

Input: x = -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Constraints: -2<sup>31</sup> <= x <= 2<sup>31</sup> - 1

Follow up: Could you solve it without converting the integer to a string?

题目大意：

判断是否回文数字

解题思路：

N/A

解题步骤：

N/A

注意事项：

Python代码：

def isPalindrome(self, x: int) -> bool:
	return str(x) == str(x)[::-1]

算法分析：

时间复杂度为O(n)，空间复杂度O(n)

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算法II解题思路：

Follow-up 不能用str，就求它的reversed数

注意事项：

1. x是用于计算过程，所以不断变化，最后一行不能用它来与reversed的结果比较

Python代码：

def isPalindrome2(self, x: int) -> bool:
	if x < 0:
		return False
	rev, original = 0, x
	while x > 0:
		rev = rev * 10 + x % 10 # 121
		x = x // 10 # 1
	return rev == original

算法分析：

时间复杂度为O(n)，空间复杂度O(1)