DCP13 - Longest Substring

let alphabet = "abcdefghijklmnopqrstuvwxyz";
let str = "abcdeaklmna";
let k = 4;

function longestSubstring(str, k){
    if(k <= 0){
        return "Error using function substring!";
    }
    let answer = "";
    for(let i=0; i<str.length-1; i++){
        // 1st index = i
        // Next variable named "permanent answer" will be in relation of this "i" index
        let permanentAnswer = str[i];
        for(let j=i+1; j<str.length; j++){
            // 2nd index = j
            // For every new letter after the first one, I have to check if its position in alphabet
            // is between the limits. I have to compare it with ALL the previous letters in my permanentAnswer
            let hits = 0;
            for(let k=0; k<permanentAnswer.length; k++){
                if( Math.abs(alphabet.indexOf(str[j]) - alphabet.indexOf(permanentAnswer[k])) <= (k-1) ){
                    hits++;
                }
            }
            // Now, "hits" must be equal to length of my permanent answer
            // This means that the letters are not too far apart
            if(hits === permanentAnswer.length){
                permanentAnswer += str[j]
            }
            else{
                // No, need to walk more in my "str" string after the 1st failure
                break;
            }
        }
        // Now, I have the permanent "longest answer" beginning from "i" index
        if(permanentAnswer.length >= answer.length){
            answer = permanentAnswer;
        }
    }
    return answer;
}

// MAIN FUNCTION
console.log(longestSubstring(str, k));