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.

bool isPalindrome(int x) 
{
    if(x < 0)
        return false;
    
    long long val = 0;
    int temp = x;
    while(x)
    {
        val = val *10 + x %10;
        x = x / 10;
    }
    
    if(val > INT_MAX || val < INT_MIN || (val != temp))
        return false;
    
    return true;
    
    
}

2021.08.24更新
更新两种更简单的方法

class Solution {
public:
    bool isPalindrome(int x) {
        if(x < 0 || (x!=0 && x%10==0)) return false;
        
        int sum = 0;
        while(x > sum)
        {
            sum = sum * 10 + x % 10;
            x = x/10;
        }
        
        return (x == sum) || (x == sum/10);
    }
};

运行效率：

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Palindrome Number.
Memory Usage: 5.9 MB, less than 72.80% of C++ online submissions for Palindrome Number.

将数字转换为字符串

class Solution {
public:
    bool isPalindrome(int x) {
        string str = to_string(x);
        int n = str.size();
        for(int i = 0;i < n/2;i++)
        {
            if(str[i] != str[n - i - 1])
                return false;
        }
        return true;

    }
};

运行效率：

执行用时：28 ms, 在所有 C++ 提交中击败了11.22%的用户
内存消耗：5.7 MB, 在所有 C++ 提交中击败了88.33%的用户