Palindrome Number

9.Palindrome Number

Given an integer x, return true if x is palindrome integer.

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

Example 1:

Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

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

个人解答：

时间复杂度：O(n)

空间复杂度：O(1)

bool isPalindrome(int x) {
    if(x < 0)return false;
    int count = 0;//x位数
	int temp = x;
	while (temp != 0) {
		temp /= 10;
		count++;
	}
	int first = pow(10, count-1);//选中首位时所需除数
	count /= 2;//只需遍历数字一半
	while (count--) {
		if (x / first != x % 10)return false;
		else {
			x %= first;
			x /= 10;
			first /= 100;
		}
	}
	return true;
}

#include <iostream>
#include <string>
#include <iomanip>

using namespace std;


class Solution {

public:
    bool is_palindrome(int value) {
        if (value < 0) return false;
        if (value < 10) return true;
        int divdend = 1;
        while (divdend < value) {
            divdend *= 10;
        }
        divdend /= 10;
        while (value != 0) {
            int first = value / divdend;
            int last = value % 10;
            if (first != last) return false;
            value = (value % divdend) / 10;
            divdend /= 100;
        }
        return true;
    }
    bool is_palindrome_str(int value) {
        if (value < 0) return false;
        string s = to_string(value);
        string backup = s;
        reverse(begin(s), end(s));
        return s == backup;
    }
};

int main(int argc, char* argv[]) {
    int value;
    Solution sol;
    while (cin >> value) {
        cout << value << " is palindrome: " << boolalpha << sol.is_palindrome_str(value) << endl;
    }
    return EXIT_SUCCESS;
}