Find missing letter in list of alphabets

Question

I am trying to solve the following issue:

Find the missing letter in the passed letter range and return it. If all letters are present in the range, return undefine

Answer 1

This is an even shorter answer thanks to RegExp() that allows you to create a Regular Expression on the fly and use match() to strip off the given letters from a generated String that has all the letters in the given range:

function fearNotLetter(str) {
  var allChars = '';
  var notChars = new RegExp('[^'+str+']','g');
  for (var i=0;allChars[allChars.length-1] !== str[str.length-1] ;i++)
    allChars += String.fromCharCode(str[0].charCodeAt(0)+i);
  return allChars.match(notChars) ? allChars.match(notChars).join('') : undefined;

}

Answer 2

Here's my another answer in missing letters:

function fearNotLetter(str) {
  var alphabet = 'abcdefghijklmnopqrstuvwxyz';
  var first = alphabet.indexOf(str[0]);
  var last = alphabet.indexOf(str[str.length-1]);
  var alpha = alphabet.slice(first,last);

  for(var i=0;i<str.length;i++){
    if(str[i] !== alpha[i]){
      return alpha[i];
    }
  } 
}

console.log(fearNotLetter("abce"));

Answer 3

I think that you wanted to say that if a string doesn't start with "a" than return "undefined". So here's my code:

 function fearNotLetter(str) {
   var alphabet = ("abcdefgheijklmnopqrstuvwxyz");
   var i = 0;
   var j = 0;
   while (i < alphabet.length && j < str.length) {
     if (alphabet.charAt(i) != str.charAt(j)) {
       i++;
       j++;
       if (alphabet.charAt(i - 1) == "a") {
         return "undefined";
       } else {
         return (alphabet.charAt(i - 1));
       }
     }
     i++;
     j++;
   }
 }

 alert(fearNotLetter('abce'));

Here's the working JsFiddle.

You wanted the code to return the missing letter so I used CharAt.
You can make an array of letters and then search through it to see if it maches with letters from the string....

Answer 4

Another function that may help:

var alphabet = "abcdefgheijklmnopqrstuvwxyz";
function fearNotLetter(a) {
  function letterIndex(text, index) {
    var letter = text.charAt(0);
    if (alphabet.indexOf(letter) !== index) { return alphabet.charAt(index); } else { return letterIndex(text.substring(1), index + 1) }
  }
  if (alphabet.indexOf(a) === -1) {
    return letterIndex(a, alphabet.indexOf(a.charAt(0)));
  }
  return undefined;
}
fearNotLetter("abc"); //Undefined
fearNotLetter("abce"); //d
fearNotLetter("fgi"); //h