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?
Solution 1
/**
* @param {number} x
* @return {boolean}
*/
var isPalindrome = function(x) {
var s = '' + x;
var l = 0;
var r = s.length - 1;
while (l < r) {
if (s[l] !== s[r]) return false;
l++;
r--;
}
return true;
};
Explain:
转成字符串，判断是否回文
Complexity:
- Time complexity : O(log(n)).
- Space complexity : O(1).
Solution 2
/**
* @param {number} x
* @return {boolean}
*/
var isPalindrome = function(x) {
if (x < 0) return false;
var num = x;
var res = 0;
while (num !== 0) {
res = (res * 10) + (num % 10);
num = Math.floor(num / 10);
}
return res === x;
};
Explain:
直接翻转数字，比较是否相等
Complexity:
- Time complexity : O(log(n)).
- Space complexity : O(1).