LeetCode-in-All
9. Palindrome Number
Easy
Given an integer x, return true if x is palindrome integer.
An integer is a palindrome when it reads the same backward as forward. For example, 121 is palindrome while 123 is not.
Example 1:
Input: x = 121
Output: true
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.
Example 3:
Input: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
Example 4:
Input: x = -101
Output: false
Constraints:
-231 <= x <= 231 - 1
Follow up: Could you solve it without converting the integer to a string?
Solution
class Solution {
/**
* @param Integer $x
* @return Boolean
*/
public function isPalindrome($x) {
if ($x < 0) {
return false;
}
$x = (string)$x;
$size = strlen($x);
if ($size % 2 == 1) {
$c = ($size - 1) / 2;
for ($i = 0; $i < $c; $i++) {
if ($i == $c) {
return true;
}
if ($x[$i] !== $x[$size - ($i + 1)]) {
return false;
}
}
return true;
} else {
$c = $size / 2;
for ($i = 0; $i < $c; $i++) {
if ($x[$i] !== $x[$size - ($i + 1)]) {
return false;
}
}
return true;
}
}
}