A.I, Data and Software Engineering

Check if a string is a palindrome


palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward, such as madamracecar.

There are also numeric palindromes, including date/time stamps using short digits 11/11/11 11:11 and long digits 02/02/2020. Sentence-length palindromes ignore capitalization, punctuation, and word boundaries, so “A man, a plan, a canal, Panama!” is treated as AMANAPLANACANALPANAMA.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false


  • s consists only of printable ASCII characters.


  • Remove all characters that is not alphanumber, e.g. ;`, . :`
  • Check if the new string equals its reverse

Kotlin implementation

#Kotlin implementation
class Solution {
    fun isPalindrome(s: String): Boolean {
        val s1 = s.toLowerCase().replace("[^a-zA-Z0-9]".toRegex(), "")
        return s1 == s1.reversed()

For more Kotlin tutorial, go here.

Java Implementation

Check by comparing chars

 static boolean isPalindrome(String str)
        // Pointers pointing to the beginning
        // and the end of the string
        int i = 0, j = str.length() - 1;
        // While there are characters toc compare
        while (i < j) {
            // If there is a mismatch
            if (str.charAt(i) != str.charAt(j))
                return false;
            // Increment first pointer and
            // decrement the other
        // Given string is a palindrome
        return true;

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