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Commit 63a3394

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algorithm: letter combinations (TheAlgorithms#1209)
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‎DIRECTORY.md‎

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* [FibonacciNumberRecursive](Recursive/FibonacciNumberRecursive.js)
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* [FloodFill](Recursive/FloodFill.js)
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* [KochSnowflake](Recursive/KochSnowflake.js)
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* [LetterCombination](Recursive/LetterCombination.js)
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* [Palindrome](Recursive/Palindrome.js)
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* [SubsequenceRecursive](Recursive/SubsequenceRecursive.js)
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* [TowerOfHanoi](Recursive/TowerOfHanoi.js)

‎Recursive/LetterCombination.js‎

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/*
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*
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* Letter Combinations of a Phone Number
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*
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* Given a string containing digits from 2-9 inclusive,
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* return all possible letter combinations that the number could represent.
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* Return the answer in any order.
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* A mapping of digits to letters (just like on the telephone buttons) is given below.
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* Note that 1 does not map to any letters.
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* More info: https://leetcode.com/problems/letter-combinations-of-a-phone-number/
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*/
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/*
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* @param {string} digits
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* @returns {string[]} all the possible combinations
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*/
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const letterCombinations = (digits) => {
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const length = digits?.length
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const result = []
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if (!length) {
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return result
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}
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const digitMap = {
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2: 'abc',
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3: 'def',
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4: 'ghi',
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5: 'jkl',
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6: 'mno',
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7: 'pqrs',
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8: 'tuv',
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9: 'wxyz'
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}
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const combinations = (index, combination) => {
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let letter
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let letterIndex
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if (index >= length) {
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result.push(combination)
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return
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}
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const digit = digitMap[digits[index]]
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letterIndex = 0
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while ((letter = digit[letterIndex++])) {
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combinations(index + 1, combination + letter)
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}
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}
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combinations(0, '')
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return result
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}
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export { letterCombinations }
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import { letterCombinations } from '../LetterCombination'
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describe('Letter Combinations', () => {
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it('should return empty array if provided string is not valid', () => {
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const result = letterCombinations('')
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expect(Array.isArray(result)).toBe(true)
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expect(result.length).toBe(0)
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})
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it('should return empty array if provided string is empty', () => {
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const result = letterCombinations(null)
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expect(Array.isArray(result)).toBe(true)
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expect(result.length).toBe(0)
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})
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it('should return letter combination of 234', () => {
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const result = letterCombinations('234')
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expect(result).toEqual([
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'adg',
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'adh',
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'adi',
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'aeg',
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'aeh',
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'aei',
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'afg',
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'afh',
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'afi',
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'bdg',
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'bdh',
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'bdi',
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'beg',
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'beh',
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'bei',
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'bfg',
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'bfh',
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'bfi',
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'cdg',
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'cdh',
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'cdi',
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'ceg',
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'ceh',
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'cei',
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'cfg',
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'cfh',
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'cfi'
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])
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})
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})

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