Problem 9 Palindrome Number

Language

JavaScript Java

Description

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

Example

Input

1. 121
2. -121

Output

1. true
2. false

Explanation

1. palindrome
2. From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Analysis

First, prevent obviously impossible number by limit range of number.
Then, compare each number in x with the corresponding number in certain position.
Last, return in boolean.

Solution

JavaScript

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function (x) {
    if (x < 0 || (x > 0 && x % 10 === 0)) {
        return false;
    }
    let rev = 0;
    while (x > rev) {
        rev = Math.floor(rev * 10 + x % 10);
        x = Math.floor(x / 10);
    }
    return x === rev || x === Math.floor(rev / 10);
};

Java

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

    }
}