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

Example 1:

Input: 121Output: true

Example 2:

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

Example 3:

Input: 10Output: falseExplanation: 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?

 

M1: 转换成string

time: O(n), space: O(n)

class Solution {    public boolean isPalindrome(int x) {        String s = Integer.toString(x);        int i = 0, j = s.length() - 1;        while(i <= j) {            if(s.charAt(i) != s.charAt(j))                return false;            i++;            j--;        }        return true;    }}

M2: 把x反转过来rev，最后如果x=rev，说明是palindrome

time: O(length of x), space: O(1)

class Solution {    public boolean isPalindrome(int x) {        if(x < 0) return false;        int rev = 0;        int xx = x;        while(xx > 0) {            rev = rev * 10 + xx % 10;            xx /= 10;        }        return x == rev;    }}