string_incrementer.md

String incrementer ^{5 Kyu}

^{LINK TO THE KATA - REGULAR EXPRESSIONS STRINGS}

Description

Your job is to write a function which increments a string, to create a new string.

• If the string already ends with a number, the number should be incremented by 1.
• If the string does not end with a number. the number 1 should be appended to the new string.

Examples:

foo -> foo1

foobar23 -> foobar24

foo0042 -> foo0043

foo9 -> foo10

foo099 -> foo100

Attention: If the number has leading zeros the amount of digits should be considered.

Solution

const getIndexFirstDigit = string => {
  for (let i = 0; i < string.length; i++) {
    const currentCharacter = string[i]
    const isInteger = Number(currentCharacter) >= 0

    if (!isInteger) return i
  }
}

const incrementString = string => {
  const reverseString = string.split('').reverse().join('')

  const indexFirstDigit = getIndexFirstDigit(reverseString)

  const stringPart = string.slice(0, -indexFirstDigit)
  const stringNumericPart = string.slice(string.length - indexFirstDigit)
  const realNumericPart = Number(stringNumericPart) + 1

  if (stringNumericPart.length === 0) return `${string}1`

  const numberZerosLeft =
    stringNumericPart.length - String(realNumericPart).length

  let result = stringPart
  if (numberZerosLeft > 0) result += '0'.repeat(numberZerosLeft)
  result += realNumericPart

  return result
}