9. Palindrome Number

Problem:

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

Input: 121
Output: true

Example 2:

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Follow up:

Coud you solve it without converting the integer to a string?

思路：

将整数由低位到高位依次压入数组中,然后比较前一半和后一半的值即可。

Solution (C++):

bool isPalindrome(int x) {
    if (x < 0) return false;
    if (x < 10)  return true;
    vector<int> vec{};
    while (x/10) {
        vec.push_back(x%10);
        x /= 10;
        if (x < 10) { vec.push_back(x); break; }
    }

    bool is_pal = true;
    for (int i = 0; i <= (vec.size()-1) / 2; ++i) {
        if (vec[i] != vec[vec.size()-1-i]) {
            is_pal = false;
            break;
        }
    }
    return is_pal;
}

性能：

Runtime: 44 ms  Memory Usage: 9.5 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB