freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69738771fb5a7b8b24cca29e.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69738771fb5a7b8b24cca29e	Challenge 172: Letters-Numbers	28	challenge-172

--description--

Given a string containing only letters and numbers, return a new string where a hyphen (-) is inserted every time the string switches from a letter to a number, or a number to a letter.

--hints--

separateLettersAndNumbers("ABC123") should return "ABC-123".

assert.equal(separateLettersAndNumbers("ABC123"), "ABC-123");

separateLettersAndNumbers("Route66") should return "Route-66".

assert.equal(separateLettersAndNumbers("Route66"), "Route-66");

separateLettersAndNumbers("H3LL0W0RLD") should return "H-3-LL-0-W-0-RLD".

assert.equal(separateLettersAndNumbers("H3LL0W0RLD"), "H-3-LL-0-W-0-RLD");

separateLettersAndNumbers("a1b2c3d4") should return "a-1-b-2-c-3-d-4".

assert.equal(separateLettersAndNumbers("a1b2c3d4"), "a-1-b-2-c-3-d-4");

--seed--

--seed-contents--

function separateLettersAndNumbers(str) {

  return str;
}

--solutions--

function separateLettersAndNumbers(str) {
  if (str.length === 0) return str;

  let result = str[0];

  for (let i = 1; i < str.length; i++) {
    const prev = str[i - 1];
    const curr = str[i];

    const prevIsLetter = /[a-zA-Z]/.test(prev);
    const currIsLetter = /[a-zA-Z]/.test(curr);

    if (prevIsLetter !== currIsLetter) {
      result += "-";
    }

    result += curr;
  }

  return result;
}