LeetCode EP.5

9. Palindrome Number

Photo by Annie Spratt on Unsplash

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:

• -231 <= x <= 231 - 1

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

思路

這裡我一開始預想是用前後輪巡的方式，所以直接把 List size/2 所以得到下面 Answer 1 的解法，Else 會這樣寫是因為 Submit 時發現 testcase 裡 0 算是回文的。

Answer 1.

這裡算是第一次解，但後來 Submit 後發現大家 Runtime 怎麼都這麼低，去看了一下別人的寫法，發現有個更優秀的直接使用 reversed 就好了。

Answer 2.

那如果想玩玩看的話也可以參考我的 Github 使用 IntelliJ 就可以 Build 了，裡面也寫了 Test 來驗證。