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refactor: redesign LetterCombinationsOfPhoneNumber
(#5221)
* 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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@ -5,49 +5,61 @@ import java.util.Collections;
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import java.util.List;
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public final class LetterCombinationsOfPhoneNumber {
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private static final char EMPTY = '\0';
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// Mapping of numbers to corresponding letters on a phone keypad
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private static final String[] KEYPAD = new String[] {" ", String.valueOf(EMPTY), "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
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private LetterCombinationsOfPhoneNumber() {
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}
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static Character[][] numberToCharMap;
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/**
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* Generates a list of all possible letter combinations that the provided
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* array of numbers could represent on a phone keypad.
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*
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* @param numbers an array of integers representing the phone numbers
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* @return a list of possible letter combinations
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*/
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public static List<String> getCombinations(int[] numbers) {
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if (numbers == null) {
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return List.of("");
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}
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return generateCombinations(numbers, 0, new StringBuilder());
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}
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protected static List<String> printWords(int[] numbers, int len, int numIndex, String s) {
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if (len == numIndex) {
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return new ArrayList<>(Collections.singleton(s));
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/**
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* Recursive method to generate combinations of letters from the phone keypad.
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*
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* @param numbers the input array of phone numbers
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* @param index the current index in the numbers array being processed
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* @param current a StringBuilder holding the current combination of letters
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* @return a list of letter combinations formed from the given numbers
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*/
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private static List<String> generateCombinations(int[] numbers, int index, StringBuilder current) {
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// Base case: if we've processed all numbers, return the current combination
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if (index == numbers.length) {
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return new ArrayList<>(Collections.singletonList(current.toString()));
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}
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List<String> stringList = new ArrayList<>();
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for (int i = 0; i < numberToCharMap[numbers[numIndex]].length; i++) {
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String sCopy = String.copyValueOf(s.toCharArray());
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sCopy = sCopy.concat(numberToCharMap[numbers[numIndex]][i].toString());
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stringList.addAll(printWords(numbers, len, numIndex + 1, sCopy));
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final var number = numbers[index];
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if (number < 0 || number > 9) {
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throw new IllegalArgumentException("Input numbers must in the range [0, 9]");
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}
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return stringList;
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}
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private static void printWords(int[] numbers) {
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generateNumberToCharMap();
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List<String> stringList = printWords(numbers, numbers.length, 0, "");
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stringList.stream().forEach(System.out::println);
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}
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List<String> combinations = new ArrayList<>();
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protected static void generateNumberToCharMap() {
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numberToCharMap = new Character[10][5];
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numberToCharMap[0] = new Character[] {'\0'};
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numberToCharMap[1] = new Character[] {'\0'};
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numberToCharMap[2] = new Character[] {'a', 'b', 'c'};
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numberToCharMap[3] = new Character[] {'d', 'e', 'f'};
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numberToCharMap[4] = new Character[] {'g', 'h', 'i'};
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numberToCharMap[5] = new Character[] {'j', 'k', 'l'};
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numberToCharMap[6] = new Character[] {'m', 'n', 'o'};
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numberToCharMap[7] = new Character[] {'p', 'q', 'r', 's'};
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numberToCharMap[8] = new Character[] {'t', 'u', 'v'};
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numberToCharMap[9] = new Character[] {'w', 'x', 'y', 'z'};
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}
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// Iterate over each letter and recurse to generate further combinations
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for (char letter : KEYPAD[number].toCharArray()) {
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if (letter != EMPTY) {
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current.append(letter);
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}
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combinations.addAll(generateCombinations(numbers, index + 1, current));
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if (letter != EMPTY) {
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current.deleteCharAt(current.length() - 1); // Backtrack by removing the last appended letter
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}
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}
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// Driver code
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public static void main(String[] args) {
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int[] number = {2, 3, 4};
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printWords(number);
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return combinations;
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}
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}
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