LeetCode: Letter Combinations Of A Phone Number Solution

1/**
2 * @param {string} digits
3 * @return {string[]}
4 */
5var letterCombinations = function (digits) {
6  const digitChars = {
7    2: "abc",
8    3: "def",
9    4: "ghi",
10    5: "jkl",
11    6: "mno",
12    7: "pqrs",
13    8: "tuv",
14    9: "wxyz",
15  }
16
17  const res = []
18
19  const recursion = (message, digitIndex) => {
20    if (digitIndex === digits.length) {
21      res.push(message)
22      return
23    }
24
25    for (const c of digitChars[digits[digitIndex]]) {
26      recursion(message + c, digitIndex + 1)
27    }
28  }
29
30  recursion("", 0)
31
32  return res.filter(Boolean)
33}