Palindrome Check

Grasp the concept of palindromes in programming and learn to check strings efficiently for this symmetry.

Strings
easy

Published At

6/4/2021

Write a function that takes in a non-empty string and that returns a boolean representing whether the string is a palindrome.

A palindrome is defined as a string that's written the same forward and backward. Note that single-character strings are palindromes.

Sample Input

js
``string = "abcdcba"``
js
``string = "abcdcba"``

Sample Output

js
``true // it's written the same forward and backward``
js
``true // it's written the same forward and backward``

Hints

Hint 1

Start by building the input string in reverse order and comparing this newly built string to the input string. Can you do this without using string concatenations?

Hint 2

Can you optimize your algorithm by using recursion? What are the implications of recursion on an algorithm's space-time complexity analysis?

Hint 3

Go back to an iterative solution and try using pointers to solve this problem: start with a pointer at the first index of the string and a pointer at the final index of the string. What can you do from there?

Optimal Space & Time Complexity

O(n) time | O(1) space - where n is the length of the input string

Solution-1
js
``````function isPalindrome(string) {
if (string.length === 1) return true;
if (string.length === 2) {
if (string[0] === string[1]) {
return true
} else return false
}
string.charAt[string.length]
if (string[0] === string[string.length - 1]) {
let sliced = string.slice(1, string.length - 1)
return isPalindrome(sliced);
}
return false
}``````
Solution-1
js
``````function isPalindrome(string) {
if (string.length === 1) return true;
if (string.length === 2) {
if (string[0] === string[1]) {
return true
} else return false
}
string.charAt[string.length]
if (string[0] === string[string.length - 1]) {
let sliced = string.slice(1, string.length - 1)
return isPalindrome(sliced);
}
return false
}``````
Solution-2
js
``````function isPalindrome(string) {
let reversedString = '';
for (let i = string.length - 1; i >= 0; i--) {
reversedString += string[i];
}
return string === reversedString;
}``````
Solution-2
js
``````function isPalindrome(string) {
let reversedString = '';
for (let i = string.length - 1; i >= 0; i--) {
reversedString += string[i];
}
return string === reversedString;
}``````

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Have a wonderful day.
Abhishek 🙏