Letter Combinations of a Phone Number

mediumcodingAlgorithmsBacktrackingStrings~30 min

Asked at Google, Meta

Overview

Given a string containing digits 2-9, return all possible letter combinations the number could represent (phone keypad mapping). Return in any order.

Mapping: 2→abc, 3→def, 4→ghi, 5→jkl, 6→mno, 7→pqrs, 8→tuv, 9→wxyz

Constraints

0 <= digits.length <= 4
digits[i] is between '2' and '9'.

Examples

letterCombinations("23");
// => ["ad","ae","af","bd","be","bf","cd","ce","cf"]

letterCombinations("");
// => []

Solution

Reveal solution

function letterCombinations(digits) {
  if (!digits.length) return [];
  const map = { '2':'abc','3':'def','4':'ghi','5':'jkl','6':'mno','7':'pqrs','8':'tuv','9':'wxyz' };
  const result = [];
  function backtrack(i, path) {
    if (i === digits.length) { result.push(path); return; }
    for (const c of map[digits[i]]) backtrack(i + 1, path + c);
  }
  backtrack(0, "");
  return result;
}

Resources

Letter Combinations of a Phone Number — LeetCode

letter-combinations-phone-number.js

Letter Combinations of a Phone Number

mediumcodingAlgorithmsBacktracking

Overview

Given a string containing digits 2-9, return all possible letter combinations the number could represent (phone keypad mapping). Return in any order.

Mapping: 2→abc, 3→def, 4→ghi, 5→jkl, 6→mno, 7→pqrs, 8→tuv, 9→wxyz

Constraints

0 <= digits.length <= 4
digits[i] is between '2' and '9'.

Examples

letterCombinations("23");
// => ["ad","ae","af","bd","be","bf","cd","ce","cf"]

letterCombinations("");
// => []

Solution

Reveal solution

function letterCombinations(digits) {
  if (!digits.length) return [];
  const map = { '2':'abc','3':'def','4':'ghi','5':'jkl','6':'mno','7':'pqrs','8':'tuv','9':'wxyz' };
  const result = [];
  function backtrack(i, path) {
    if (i === digits.length) { result.push(path); return; }
    for (const c of map[digits[i]]) backtrack(i + 1, path + c);
  }
  backtrack(0, "");
  return result;
}

Resources

Letter Combinations of a Phone Number — LeetCode

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