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refactor: redesign LetterCombinationsOfPhoneNumber (#5221)

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* Refactor

* fix clang

* fix clang

* fix clang tests

* fix pattern

* add test case null

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/test/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumberTest.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* rename MAP_OF_CHARS to KEYPAD

* fix clang

* remove main

* add tests

* feat: throw for wrong inputs

* change keypad to list

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* fix with number 1 (empty value), and add tests

* style: avoid concatenation while populating `KEYPAD`

* change to assertEquals

---------

Co-authored-by: Samuel Facchinello <samuel.facchinello@piksel.com>
Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>
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Samuel Facchinello 2024-06-13 19:40:12 +02:00 committed by GitHub
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2 changed files with 71 additions and 67 deletions
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78
src/main/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumber.java
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@ -5,49 +5,61 @@ import java.util.Collections;
import java.util.List;
public final class LetterCombinationsOfPhoneNumber {
private static final char EMPTY = '\0';
// Mapping of numbers to corresponding letters on a phone keypad
private static final String[] KEYPAD = new String[] {" ", String.valueOf(EMPTY), "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
private LetterCombinationsOfPhoneNumber() {
}
static Character[][] numberToCharMap;
protected static List<String> printWords(int[] numbers, int len, int numIndex, String s) {
if (len == numIndex) {
return new ArrayList<>(Collections.singleton(s));
/**
* Generates a list of all possible letter combinations that the provided
* array of numbers could represent on a phone keypad.
*
* @param numbers an array of integers representing the phone numbers
* @return a list of possible letter combinations
*/
public static List<String> getCombinations(int[] numbers) {
if (numbers == null) {
return List.of("");
}
return generateCombinations(numbers, 0, new StringBuilder());
}
List<String> stringList = new ArrayList<>();
for (int i = 0; i < numberToCharMap[numbers[numIndex]].length; i++) {
String sCopy = String.copyValueOf(s.toCharArray());
sCopy = sCopy.concat(numberToCharMap[numbers[numIndex]][i].toString());
stringList.addAll(printWords(numbers, len, numIndex + 1, sCopy));
}
return stringList;
/**
* Recursive method to generate combinations of letters from the phone keypad.
*
* @param numbers the input array of phone numbers
* @param index the current index in the numbers array being processed
* @param current a StringBuilder holding the current combination of letters
* @return a list of letter combinations formed from the given numbers
*/
private static List<String> generateCombinations(int[] numbers, int index, StringBuilder current) {
// Base case: if we've processed all numbers, return the current combination
if (index == numbers.length) {
return new ArrayList<>(Collections.singletonList(current.toString()));
}
private static void printWords(int[] numbers) {
generateNumberToCharMap();
List<String> stringList = printWords(numbers, numbers.length, 0, "");
stringList.stream().forEach(System.out::println);
final var number = numbers[index];
if (number < 0 || number > 9) {
throw new IllegalArgumentException("Input numbers must in the range [0, 9]");
}
protected static void generateNumberToCharMap() {
numberToCharMap = new Character[10][5];
numberToCharMap[0] = new Character[] {'\0'};
numberToCharMap[1] = new Character[] {'\0'};
numberToCharMap[2] = new Character[] {'a', 'b', 'c'};
numberToCharMap[3] = new Character[] {'d', 'e', 'f'};
numberToCharMap[4] = new Character[] {'g', 'h', 'i'};
numberToCharMap[5] = new Character[] {'j', 'k', 'l'};
numberToCharMap[6] = new Character[] {'m', 'n', 'o'};
numberToCharMap[7] = new Character[] {'p', 'q', 'r', 's'};
numberToCharMap[8] = new Character[] {'t', 'u', 'v'};
numberToCharMap[9] = new Character[] {'w', 'x', 'y', 'z'};
List<String> combinations = new ArrayList<>();
// Iterate over each letter and recurse to generate further combinations
for (char letter : KEYPAD[number].toCharArray()) {
if (letter != EMPTY) {
current.append(letter);
}
combinations.addAll(generateCombinations(numbers, index + 1, current));
if (letter != EMPTY) {
current.deleteCharAt(current.length() - 1); // Backtrack by removing the last appended letter
}
}
// Driver code
public static void main(String[] args) {
int[] number = {2, 3, 4};
printWords(number);
return combinations;
}
}

58
src/test/java/com/thealgorithms/strings/LetterCombinationsOfPhoneNumberTest.java
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@ -1,45 +1,37 @@
package com.thealgorithms.strings;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;
import java.util.Arrays;
import java.util.List;
import org.junit.jupiter.api.Test;
import java.util.stream.Stream;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.Arguments;
import org.junit.jupiter.params.provider.MethodSource;
public class LetterCombinationsOfPhoneNumberTest {
@Test
public void letterCombinationsOfPhoneNumber() {
LetterCombinationsOfPhoneNumber.generateNumberToCharMap();
@ParameterizedTest
@MethodSource("provideTestCases")
public void testLetterCombinationsOfPhoneNumber(int[] numbers, List<String> expectedOutput) {
assertEquals(expectedOutput, LetterCombinationsOfPhoneNumber.getCombinations(numbers));
}
// ** Test 1 **
// Input: digits = ""
// Output: []
int[] numbers1 = {};
List<String> output1 = Arrays.asList("");
assertTrue(LetterCombinationsOfPhoneNumber.printWords(numbers1, numbers1.length, 0, "").equals(output1));
@ParameterizedTest
@MethodSource("wrongInputs")
void throwsForWrongInput(int[] numbers) {
assertThrows(IllegalArgumentException.class, () -> LetterCombinationsOfPhoneNumber.getCombinations(numbers));
}
// ** Test 2 **
// Input: digits = "2"
// Output: ["a","b","c"]
int[] numbers2 = {2};
List<String> output2 = Arrays.asList("a", "b", "c");
assertTrue(LetterCombinationsOfPhoneNumber.printWords(numbers2, numbers2.length, 0, "").equals(output2));
private static Stream<Arguments> provideTestCases() {
return Stream.of(Arguments.of(null, List.of("")), Arguments.of(new int[] {}, List.of("")), Arguments.of(new int[] {2}, List.of("a", "b", "c")), Arguments.of(new int[] {2, 3}, List.of("ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf")),
Arguments.of(new int[] {2, 3, 4}, List.of("adg", "adh", "adi", "aeg", "aeh", "aei", "afg", "afh", "afi", "bdg", "bdh", "bdi", "beg", "beh", "bei", "bfg", "bfh", "bfi", "cdg", "cdh", "cdi", "ceg", "ceh", "cei", "cfg", "cfh", "cfi")),
Arguments.of(new int[] {3, 3}, List.of("dd", "de", "df", "ed", "ee", "ef", "fd", "fe", "ff")), Arguments.of(new int[] {8, 4}, List.of("tg", "th", "ti", "ug", "uh", "ui", "vg", "vh", "vi")), Arguments.of(new int[] {2, 0}, List.of("a ", "b ", "c ")),
Arguments.of(new int[] {9, 2}, List.of("wa", "wb", "wc", "xa", "xb", "xc", "ya", "yb", "yc", "za", "zb", "zc")), Arguments.of(new int[] {0}, List.of(" ")), Arguments.of(new int[] {1}, List.of("")), Arguments.of(new int[] {2}, List.of("a", "b", "c")),
Arguments.of(new int[] {1, 2, 0, 4}, List.of("a g", "a h", "a i", "b g", "b h", "b i", "c g", "c h", "c i")));
}
// ** Test 3 **
// Input: digits = "23"
// Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
int[] numbers3 = {2, 3};
List<String> output3 = Arrays.asList("ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf");
assertTrue(LetterCombinationsOfPhoneNumber.printWords(numbers3, numbers3.length, 0, "").equals(output3));
// ** Test 4 **
// Input: digits = "234"
// Output: ["adg", "adh", "adi", "aeg", "aeh", "aei", "afg", "afh", "afi",
// "bdg", "bdh", "bdi", "beg", "beh", "bei", "bfg", "bfh", "bfi", "cdg", "cdh",
// "cdi", "ceg", "ceh", "cei", "cfg", "cfh", "cfi"]
int[] numbers4 = {2, 3, 4};
List<String> output4 = Arrays.asList("adg", "adh", "adi", "aeg", "aeh", "aei", "afg", "afh", "afi", "bdg", "bdh", "bdi", "beg", "beh", "bei", "bfg", "bfh", "bfi", "cdg", "cdh", "cdi", "ceg", "ceh", "cei", "cfg", "cfh", "cfi");
assertTrue(LetterCombinationsOfPhoneNumber.printWords(numbers4, numbers4.length, 0, "").equals(output4));
private static Stream<Arguments> wrongInputs() {
return Stream.of(Arguments.of(new int[] {-1}), Arguments.of(new int[] {10}), Arguments.of(new int[] {2, 2, -1, 0}), Arguments.of(new int[] {0, 0, 0, 10}));
}
}