Palindrome Puzzles – Popular Interview Question?

Every kid is dazzled at palindromes. It’s the same word or sentence backwards! What black magic is this? With my name being Adam, I couldn’t escape “Madam Im Adam.”

Who knew that decades later this would be a popular interview question for programmers?

There is a super duper easy way to solve this, with a pretty brief function.

//Needed to get the lowercased function
import Foundation

//Input a string and output true or false
func checkIfPalindrome(phrase: String) -> Bool {
    //Remove spaces and make everything lowercase (palindromes are case insensitive)
    var cleanPhrase = phrase.replacingOccurrences(of: " ", with: "").lowercased()
    //Compare the cleanPhrase to the reverse of it (which must be converted to String)
    return cleanPhrase == String(cleanPhrase.reversed())
}

print(checkIfPalindrome(phrase: "Madam Im Adam"))
//True

What about other symbols, like the apostrophe in I’m? This would break it, so if I wanted to be thorough I’d have to remove all non-letter characters.

But when you get asked about palindromes, usually using built in functions leads to… “Oh that’s nice, now try it a different way.”

import Foundation

func checkIfPalindrome(phrase: String) -> Bool {
    
    var cleanPhrase = phrase.replacingOccurrences(of: " ", with: "").lowercased()
    //Set up a blank array of characters
    var reversedPhraseArr = [Character]()
    //Iterate through each character of the phrase
    for c in cleanPhrase {
        //For the first character, just add it into the blank character array.
        if reversedPhraseArr.count == 0 {
            reversedPhraseArr.append(c)
        //For every new character, add it in the first position of the array 
        } else {
            reversedPhraseArr.insert(c, at: 0)
        }
    }
    //Turn the character array back to a string
    let reversedPhrase = String(reversedPhraseArr)
    //Finally do a comparison
    return cleanPhrase == reversedPhrase
}

print(checkIfPalindrome(phrase: "Madam Im Adam"))
//True

The first is pretty easy to remember. The second one has a bunch of more steps. That’s why it is always a one-two punch.

Then again, I’m sure there is a third punch on using a better Big O notation and increasing the speed efficiency of this function. That will be another day…