LeetCode Palindrome Number（009）解法總結

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複製程式碼

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.複製程式碼

Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.複製程式碼

Follow up:

Coud you solve it without converting the integer to a string?

思路

對於這種簡單的逆序問題，將輸入轉化為StringBuffer物件，再呼叫逆置函式即可。

但是題目要求不能轉換為字串，所以要從整型下手。

1. 當數字為負數時，是肯定不滿足要求的。
2. 當數字為正數或0時，只要保證每位數字從高到低的權重*數字之和，等於每位數字從低到高的權重*數字之和，說明這個正數是對稱的。

class Solution {
    public boolean isPalindrome(int x) {
        boolean flag = true;
        if(x < 0){
            flag = false;
        }
        
        //數字逆置過程
        int temp = x, out = 0;
        while(temp != 0){
            out = out * 10 + temp % 10;
            temp = temp / 10;
        }
        
        if(x != out){
            flag = false;
        }
        
        return flag;
    }
}複製程式碼