FreeCodeCamp => Algorithms: No Repeats Please

fcc-algo-noRepeat.js

/**
 * @param {array} arr  array to insert into
 * @param {number} i  index for insertion
 * @param {object} val value to be inserted
 * @return {array} a new array with val inserted at i
 */
const insert = (i, arr, val) => [...arr.slice(0, i), val, ...arr.slice(i)];

/**
 * @param {string} 
 * @return {array} array of permutations
 */
const getPermutations = (str) => {
  let strArray = str.split('');
  let permutations = [[]];

  strArray.forEach((curChar, i) => {
    let tempArray = [];
    
    permutations.forEach((val) => {
      for (let j = 0; j <= val.length; j++) {
        tempArray.push(insert(j, val, curChar));
      }
    });
    
    permutations = tempArray.slice();
  });

  return permutations
      .map((val) => val.join(''));
};

/**
 * @param {string} str
 * @return {number} number of total permutations of the provided string
 *   that don't have repeated consecutive letters
 */
function permAlone(str) {
  const repeatRe = /(\w{1})\1/i;
  const noRepeat = (val) => !repeatRe.test(val);
  const permutations = getPermutations(str);

  return permutations
    .filter(noRepeat)
    .length;
}

// console.log(
//   `aab: ${permAlone('aab')}`
// )
// console.log(
//   `aabb: ${permAlone('aabb')}`
// )
// console.log(
//   `ab: ${permAlone('ab')}`
// )
// console.log(
//   `aaabb: ${permAlone('aaabb')}`
// )
console.log(
  `123: ${permAlone('123')}`
)