17. Letter Combinations of a Phone Number

Author: antisilent

solutions/0017-letter-combinations-of-a-phone-number/README.md

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+# [17. Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/) [🟡](## "Medium")
+
+## Description:
+
+Given a string containing digits from `2-9` inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
+
+A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
+
+    2: 'abc'
+    3: 'def'
+    4: 'ghi'
+    5: 'jkl'
+    6: 'mno'
+    7: 'pqrs'
+    8: 'tuv'
+    9: 'wxyz'
+
+### Example 1:
+
+    Input: digits = "23"
+    Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
+
+### Example 2:
+
+    Input: digits = ""
+    Output: []
+
+### Example 3:
+
+    Input: digits = "2"
+    Output: ["a","b","c"]
+
+### Constraints:
+
+* `0 <= digits.length <= 4`
+* `digits[i]` is a digit in the range `['2', '9']`.

solutions/0017-letter-combinations-of-a-phone-number/solution.js

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+/**
+ * @param {string} digits
+ * @return {string[]}
+ */
+const map = {
+  2: 'abc',
+  3: 'def',
+  4: 'ghi',
+  5: 'jkl',
+  6: 'mno',
+  7: 'pqrs',
+  8: 'tuv',
+  9: 'wxyz',
+};
+
+export default function letterCombinations(digits, result = [], idx = 0, str = '') {
+  if (!digits) return [];
+
+  if (idx === digits.length) {
+    result.push(str);
+    return;
+  } else {
+    let letters = map[digits[idx]];
+    for (let i = 0; i < letters.length; i++) {
+      letterCombinations(digits, result, idx + 1, str + letters[i]);
+    }
+  }
+
+  return result;
+};

solutions/0017-letter-combinations-of-a-phone-number/solution.test.js

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+import solution from './solution';
+
+describe('17. Letter Combinations of a Phone Number', () => {
+  const cases = [
+    ['23', ['ad','ae','af','bd','be','bf','cd','ce','cf']],
+    ['', []],
+    ['2', ['a','b','c']],
+  ];
+
+  for (const [i, [input, expected]] of cases.entries()) {
+    it(`Case ${i + 1}`, () => {
+      expect(solution(input)).toStrictEqual(expected);
+    });
+  }
+});