LeetCode/C++/palindrome-number.cpp at master · TreHack/LeetCode · GitHub

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// Time:  O(logx) = O(1)
// Space: O(1)

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

// Time:  O(logx) = O(1)
// Space: O(1)
class Solution2 {
public:
    bool isPalindrome(int x) {
        if(x < 0) {
            return false;
        }

        int divisor = 1;
        while (x / divisor >= 10) {
            divisor *= 10;
        }

        for (; x > 0; x = (x % divisor) / 10, divisor /= 100) {
            int left = x / divisor;
            int right = x % 10;
            if (left != right) {
                return false;
            }
        }

        return true;
    }
};