JavaScript: Letter combinations of a number

JavaScript Function: Exercise-13 with Solution

Letter Combinations from Digits

A string consists of digits ranging from 2 to 9, inclusive. Write a JavaScript program to get all possible letter combinations that represent the number using recursion.

Letter Combination:
1: 'abc',
2: 'def',
3: 'ghi',
4: 'jkl',
5: 'mno',
6: 'pqr',
7: 'stu',
8: 'vwx'
9: 'yz'

Test Data:
("12") -> ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
("9") -> ["y", "z"]

Sample Solution-1:

JavaScript Code:

// Function to generate letter combinations for a given digit string
const letterCombinations = (digits) => {
 const length = digits?.length; // Get the length of the input digits
 const result = []; // Initialize an array to store the combinations
 // Base case: If the input digits are empty, return an empty array
 if (!length) {
 return result;
 }
 // Map of digits to corresponding letters on a phone keypad
 const digitMap = {
 1: 'abc',
 2: 'def',
 3: 'ghi',
 4: 'jkl',
 5: 'mno',
 6: 'pqr',
 7: 'stu',
 8: 'vwx',
 9: 'yz',
 };
 // Recursive function to generate combinations
 const generateCombinations = (index, combination) => {
 let letter;
 let letterIndex;
 // If the index exceeds the length, add the combination to the result array
 if (index>= length) {
 result.push(combination);
 return;
 }
 // Get the letters corresponding to the current digit
 const digit = digitMap[digits[index]];
 // Iterate through each letter and recursively generate combinations
 letterIndex = 0;
 while ((letter = digit[letterIndex++])) {
 generateCombinations(index + 1, combination + letter);
 }
 };
 // Start generating combinations from the first digit
 generateCombinations(0, '');
 // Return the final array of combinations
 return result;
};
// Test the function with different input digits
console.log(letterCombinations("12")); // Output: ['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf']
console.log(letterCombinations("9")); // Output: ['yw', 'yx', 'yy', 'zw', 'zx', 'zy']

Output:

["ad","ae","af","bd","be","bf","cd","ce","cf"]
["y","z"]

Flowchart:

Flowchart: JavaScript recursion function- Letter combinations of a number.

Live Demo:

See the Pen javascript-recursion-function-exercise-13 by w3resource (@w3resource) on CodePen.

Sample Solution-2:

JavaScript Code:

const letterCombinations = (digits) => {
 const digitMap = {
 1: 'abc',
 2: 'def',
 3: 'ghi',
 4: 'jkl',
 5: 'mno',
 6: 'pqr',
 7: 'stu',
 8: 'vwx',
 9: 'yz',
 };
 const backtrack = (index, currentCombination) => {
 if (index === digits.length) {
 result.push(currentCombination);
 return;
 }
 const currentDigit = digits[index];
 const letters = digitMap[currentDigit];
 for (const letter of letters) {
 backtrack(index + 1, currentCombination + letter);
 }
 };
 const result = [];
 if (digits) {
 backtrack(0, '');
 }
 return result;
};
// Test the function with different input digits
console.log(letterCombinations("12")); // Output: ['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf']
console.log(letterCombinations("9")); // Output: ['yw', 'yx', 'yy', 'zw', 'zx', 'zy']

Output:

["ad","ae","af","bd","be","bf","cd","ce","cf"]
["y","z"]

Flowchart:

Flowchart: JavaScript recursion function- Letter combinations of a number.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that recursively generates all letter combinations for a given digit string based on telephone keypad mapping.
• Write a JavaScript function that returns all possible letter combinations from digits using recursion and backtracking.
• Write a JavaScript function that handles edge cases such as empty input and invalid digits while generating letter combinations recursively.
• Write a JavaScript function that recursively computes letter combinations for digits and removes any duplicate results.

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