Completed naive solution for phoneKeyPadMatch.

Author: simdi

recursion/index.js

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+/* 
+* @author: Chisimdi Damian Ezeanieto
+* @data: 11/03/2023
+*/
+
+// Given an input '23', return all possible character match in a key pad match
+// e.g input: '23', output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
+const phoneDigits = {
+  "2": ['a', 'b', 'c'],
+  "3": ['d', 'e', 'f'],
+  "4": ['g', 'h', 'i'],
+  "5": ['j', 'k', 'l'],
+  "6": ['m', 'n', 'o'],
+  "7": ['p', 'q', 'r', 's'],
+  "8": ['t', 'u', 'v'],
+  "9": ['w', 'x', 'y', 'z'],
+};
+const phoneKeyPadMatch = (digit) => {
+  const firstDigit = digit[0];
+  const remainingDigit = digit.substring(1);
+
+  let chars = [];
+  phoneDigits[firstDigit].map(firstChar => {
+    for (let i = 0; i < remainingDigit.length; i++) {
+      let remainingPhoneDigit = phoneDigits[remainingDigit[i]];
+
+      const combination = remainingPhoneDigit.map(comb => firstChar + comb);
+      chars.push(combination);
+    }
+  });
+  return chars.flatMap(x => x);
+};
+
+module.exports = phoneKeyPadMatch;

recursion/test.js

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+/*
+* @author: Chisimdi Damian Ezeanieto
+* @date: 11/03/2023
+*/
+const phoneKeyPadMatch = require('./index');
+
+describe('Phone key pad match', () => {
+  test('phoneKeyPadMatch function is defined', () => {
+    expect(typeof phoneKeyPadMatch).toEqual('function');
+  });
+  test('Calculate correct phoneKeyPadMatch value for "23" === ["ad","ae","af","bd","be","bf","cd","ce","cf"]', () => {
+    expect(phoneKeyPadMatch('23')).toEqual(["ad","ae","af","bd","be","bf","cd","ce","cf"]);
+  });
+  test("Calculate correct phoneKeyPadMatch value for '234' === [ 'ad', 'ae', 'af', 'ag','ah', 'ai', 'bd', 'be','bf', 'bg', 'bh', 'bi','cd', 'ce', 'cf', 'cg','ch', 'ci']", () => {
+    expect(phoneKeyPadMatch('234')).toEqual([
+      'ad', 'ae', 'af', 'ag','ah', 'ai', 'bd', 'be','bf', 'bg', 'bh', 'bi','cd', 'ce', 'cf', 'cg','ch', 'ci'
+    ]);
+  });
+  test("Calculate correct phoneKeyPadMatch value for 'aaaa' & 'aa' === ['dg', 'dh', 'di', 'eg', 'eh', 'ei', 'fg', 'fh', 'fi']", () => {
+    expect(phoneKeyPadMatch('34')).toEqual(['dg', 'dh', 'di', 'eg', 'eh', 'ei', 'fg', 'fh', 'fi']);
+  });
+});