【LeetCode】9. Palindrome Number Python3解法

题目描述：

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

例子：

Example 1:

Input: 121
Output: true
           

Example 2:

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

思路：

比较暴力一点的就是转成string方法，不过这样很简单没什么意义。如果不用转换string方法，我们可以先计算这个数字的位数，然后通过取余并乘上10的位数减1次方。这样就可以计算出最后的结果。直接上代码！

代码：

class Solution:
    def isPalindrome(self, x: int) -> bool:
        if x < 0: return False
        num = x
        check = x
        res = 0
        c = 0
        while x > 0:
            x = x // 10
            c += 1
        while num > 0:
            res += (num % 10) * (10**(c-1))
            num = num // 10
            c -= 1
        if res == check:
            return True
        else:
            return False
           

知识点：

求一个数的位数，一是转换成string然后用len()求，二就是这种方法。

c = 0 while x > 0: x = x // 10 c += 1