imperative variants

variants-im.js

module.exports = getVariants

function getVariants(str = '', symbol = '.') {
  const variants = [str]
  const bitsLength = str.length - 1

  if (bitsLength === -1) {
    return []
  }

  if (bitsLength === 0) {
    return variants
  }

  const bitsArray = new Array(bitsLength)
  bitsArray[0] = 1
  let bitsSum = 1

  while (bitsSum > 0) {
    let strWithSymbol = ''
    let currentSum = 0
    let carryBit = 1
    let pos = 0

    while (pos < bitsLength) {
      const currentBit = bitsArray[pos]
      const charWithSymbol = currentBit ? `${str[pos]}${symbol}` : str[pos]
      strWithSymbol += charWithSymbol

      if (carryBit) {
        bitsArray[pos] = currentBit ? 0 : 1
        carryBit = currentBit
      }

      currentSum += bitsArray[pos] || 0
      pos++
    }

    bitsSum = currentSum
    variants.push(strWithSymbol + str[pos])
  }

  return variants
}