題目描述

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

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.

想法

• 想法一：把整數(shù)轉(zhuǎn)換成字符串然后從中心往兩邊依次判斷
• 想法二：把整數(shù)轉(zhuǎn)過(guò)來(lái)，但是這會(huì)有一個(gè)問(wèn)題就是反過(guò)來(lái)的數(shù)可能超過(guò)了int的范圍
• 想法三：把整數(shù)的后半部分轉(zhuǎn)過(guò)來(lái)，跟前半部分進(jìn)行比較，那么這里就有一個(gè)問(wèn)題就是如何判斷整數(shù)已經(jīng)到了一半，那就是從后面拿數(shù)拿出來(lái)的數(shù)比拿掉后的大了就已經(jīng)達(dá)到了一半

代碼

public boolean isPalindrome(int x) {
        if(x < 0 || (x % 10 == 0 && x != 0)) {
            return false;
        }
        int revertedNumber = 0;
        while(x > revertedNumber) {
            revertedNumber = revertedNumber * 10 + x % 10;
            x /= 10;
        }
        return x == revertedNumber || x == revertedNumber/10;
//可能是奇數(shù)也可能偶數(shù)
    }