0009 - Palindrome Number (Easy)

Problem Link

https://leetcode.com/problems/palindrome-number/

Problem Statement

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 a palindrome while 123 is not.

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.

Example 3:

Input: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Constraints:

• -2^31 <= x <= 2^31 - 1

Approach 1: Convert to string

Convert the integer value to string format and compare it one by one.

Python

Written by @tostream

class Solution:
    def isPalindrome(self, x: int) -> bool:
        #str: convert to string
        #[::-1]: read from the end
        return str(x) == str(x)[::-1]

Java

Written by @ganajayant

class Solution {
    public boolean isPalindrome(int x) {
        String str = Integer.toString(x);
        StringBuilder rev = new StringBuilder(str).reverse();
        return rev.toString().equals(str);
    }
}

JavaScript

Written by @radojicic23

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    var str = x.toString();
    return str.split("").reverse().join("") == x.toString();
};

C++

Written by @radojicic23

class Solution {
public:
    bool isPalindrome(int x) {
        string strX = to_string(x);
        reverse(strX.begin(), strX.end());
        return to_string(x) == strX;
    }
};

Approach 2: Calculation

Calculate the reversed number.

In JavaScript, we have used Object.is(..) for value comparison, It's a ES6 feature and makes value comparisons in an even more strict fashion than the === comparison.

References from MDN and You Don't Know JS (Behind the scenes polyfills of Object.is).

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is

https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch6.md#objectis-static-function

https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/es6%20%26%20beyond/ch1.md#shimspolyfills

Python

Written by @tostream

class Solution:
    def isPalindrome(self, x: int) -> bool:
        in_num = x
        reverser = 0
        while in_num > 0:
            reverser = reverser * 10 + checker % 10
            in_num = in_num//10
        return reverser == x

Java

Written by @ganajayant

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

JavaScript

Written by @MithunPrabhu777

var isPalindrome = function(x) {
    if (x < 0 || x > 0 && Object.is(x % 10, 0)) return false;
    let n = x;
    let num = 0;
    while (x > 0) {
        num = (num * 10) + (x % 10);
        x = Math.floor(x / 10);
    }
    return Object.is(n, num);
};

C++

Written by @radojicic23

class Solution {
public:
    bool isPalindrome(int x) {
        long int res = 0, carry, n = x;
        if (x < 0) {
            return false;
        } else {
            while (n > 0) {
                carry = n % 10;
                res = res * 10 + carry;
                n /= 10;
            }
        }
        return res == x;
    }
};