firstNonRepeatingLetter.md

First non-repeating character

• Write a function named first_non_repeating_letter that takes a string input, and returns the first character that is not repeated anywhere in the string.

• For example, if given the input 'stress', the function should return 't', since the letter t only occurs once in the string, and occurs first in the string.

• As an added challenge, upper- and lowercase letters are considered the same character, but the function should return the correct case for the initial letter. For example, the input 'sTreSS' should return 'T'.

• If a string contains all repeating characters, it should return an empty string ("") or None -- see sample tests.

Examples:

firstNonRepeatingLetter('a') // 'a'
firstNonRepeatingLetter('stress') // 't'

Solutions:

function firstNonRepeatingLetter(s) {
  let res = "";
  let str = s.toLowerCase();
  for (let i = 0; i < s.length; i++) {
    if (str.indexOf(str.charAt(i)) == str.lastIndexOf(str.charAt(i))) {
      res = s.charAt(i);
      break;
    }
  }
  return res;
} 
console.log(firstNonRepeatingLetter("sTress")); // 'T'
console.log(firstNonRepeatingLetter("moonmen")); // 'e'
console.log(firstNonRepeatingLetter("moonmeen")); // ''