leetcode 9. 回文数

leetcode

1，O(n)
C++：

class Solution {
public:
    bool isPalindrome(int x) {

        if ( x < 0 ) {

            return false;
        }

        std::vector<int> numbers;
        int rest = x;
        while ( rest ) {

            int number = rest % 10;
            numbers.push_back(number);
            rest = rest / 10;
        }

        int i = 0;
        int j = numbers.size() - 1;
        while ( i < j ) {

            if ( numbers[i] != numbers[j] ) {

                return false;
            }

            ++i;
            --j;
        }

        return true;
    }
};

1，O(1)
C++：

class Solution {
public:
    bool isPalindrome(int x) {

        if ( x < 0 || ( x % 10 == 0 && x != 0 ) ) {

            return false;
        }

        int reversedNumber = 0;
        while ( x > reversedNumber ) {

            reversedNumber = reversedNumber * 10 + x % 10;
            x /= 10;
        }

        return ( x == reversedNumber || x == reversedNumber / 10 );
    }
};