palindromeIndex.js

// source: https://www.hackerrank.com/challenges/palindrome-index/problem
// video: https://youtu.be/IoiYMKmvuPQ
function isPalindrome(s){
    let left = 0
    let right = s.length - 1
    while(left < right){ // O(n)
        if(s[left]!==s[right]){
            return false
        }
        left++
        right--
    }
    return true
}

function palindromeIndex(s) {
    // Check from both ends for palindrome, allowing for 1 error
    let left = 0
    let right = s.length - 1
    while(left < right){ // O(n)
        if(s[left] !== s[right]){
            // Found error!
            // We just don't know which side has the error, so just check both
            if(isPalindrome(s.slice(left + 1, right + 1))){
                return left
            }else if(isPalindrome(s.slice(left, right))){
                return right
            }
            return -1 // There was more than one error
        }
        left++
        right--
    }
    // Total Time Complexity = O(n)
    return -1 // Result was a palindrome without error
}