【leetcode刷题笔记】009.Palindrome Num

日期：20180912

题目描述：

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.

Follow up:

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

详解：

新开了一个数组，把每一位存起来，思路很简单，代码如下：

class Solution {
public:
    bool isPalindrome(int x) {
        int a[10];
        bool isneg = false,res = true;
        if(x<0){
            return false;
        }
        int i = 0;
        for(;x!=0;i++){
            a[i] = x%10;
            x /= 10;
        }
        int j = 0;
        i--;
        while(j<i){
            if(a[j]!=a[i]){
                res = false;
            }
            j++;
            i--;
        }
        return res;
    }
};

最后我的用时256ms，最靠前的代码112ms，那究竟是怎么实现的呢。

class Solution {
public:
    bool isPalindrome(int x) {
        if(x < 0)
        {
            return false;
        }
        int test = x;
        int reverse = 0;
        while(test)
        {
            reverse = test%10 + 10*reverse;
            test = test/10;
        }
        return reverse == x;
        
    }
};

新建了一个变量，通过循环，让它等于x的反转，然后判断它和x是不是相等。我怎么就没想到，一定是因为我一边喝酒一边写代码。

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