【LeetCode】Palindrome Number

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.

首先提升int到long long int，因为int的逆序可能超过INT_MAX。

然后求出x的逆序数y，判断两者是否相等即可。

class Solution {
public:
    bool isPalindrome(int x) {
        if(x < 0)
            return false;
        else
            return Helper(x);
    }
    bool Helper(long long int x)    //incase of overflow
    {
        long long int t = x;
        long long int y = 0;
        while(t)
        {
            y = y*10 + t%10;
            t /= 10;
        }
        return (y == x);
    }
};