JavaScript: The longest palindrome in a specified string

Last update on May 30 2022 10:02:39 (UTC/GMT +8 hours)

JavaScript Function: Exercise-27 with Solution

Write a JavaScript function that returns the longest palindrome in a given string.

Note: According to Wikipedia "In computer science, the longest palindromic substring or longest symmetric factor problem is the problem of finding a maximum-length contiguous substring of a given string that is also a palindrome. For example, the longest palindromic substring of "bananas" is "anana". The longest palindromic substring is not guaranteed to be unique; for example, in the string "abracadabra", there is no palindromic substring with length greater than three, but there are two palindromic substrings with length three, namely, "aca" and "ada".
In some applications it may be necessary to return all maximal palindromic substrings (that is, all substrings that are themselves palindromes and cannot be extended to larger palindromic substrings) rather than returning only one substring or returning the maximum length of a palindromic substring.

Pictorial Presentation:

JavaScript: The longest palindrome in a specified string

Sample Solution: -

HTML Code:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Write a JavaScript function that returns the longest palindrome in a given string</title>
</head>
<body>

</body>
</html>

JavaScript Code:

function is_Palindrome(str1) {
var rev = str1.split("").reverse().join("");
return str1 == rev;
}

function longest_palindrome(str1){

var max_length = 0,
maxp = '';

for(var i=0; i < str1.length; i++) 
{
var subs = str1.substr(i, str1.length);

for(var j=subs.length; j>=0; j--) 
{
var sub_subs_str = subs.substr(0, j);
if (sub_subs_str.length <= 1)
continue;

if (is_Palindrome(sub_subs_str))
{
if (sub_subs_str.length > max_length) 
{
max_length = sub_subs_str.length;
maxp = sub_subs_str;
}
}
}
}

return maxp;
}
console.log(longest_palindrome("abracadabra"));

console.log(longest_palindrome("HYTBCABADEFGHABCDEDCBAGHTFYW12345678987654321ZWETYGDE"));

Output:

aca
12345678987654321

Flowchart:

Live Demo:

See the Pen JavaScript - The longest palindrome in a specified string-function-ex- 27 by w3resource (@w3resource) on CodePen.

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JavaScript: Tips of the Day

How to insert an item into an array at a specific index (JavaScript)?

What you want is the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert). In this example we will create an array and add an element to it into index 2:

var arr = []; arr[0] = "Jani"; arr[1] = "Hege"; arr[2] = "Stale"; arr[3] = "Kai Jim"; arr[4] = "Borge"; console.log(arr.join()); arr.splice(2, 0, "Lene"); console.log(arr.join());

Ref: https://bit.ly/2BXbp04