[LeetCode 9] Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

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Some hints:
Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

Diffculty
Easy

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[LeetCode ] Palindrome Linked List Easy

Analysis

不断地取第一位和最后一位（10进制下）进行比较，相等则取第二位和倒数第二位，直到完成比较或者中途找到了不一致的位。 可以避免造成溢出，因为只是首尾digit比较。

class Solution { public: bool isPalindrome(int x) { // negative number is not palimdrome if(x < 0) return false; int div = 1; while(x / div >= 10){ div *= 10; }

    while(x > 0){
        int lastdigit = x % 10;
        int firstdigit = (x / div) % 10;
        if(lastdigit != firstdigit)
            return false;
        x = (x % div) / 10;
        div /= 100;

    }
    return true;
}

};