Letter combination of Phone Numbers LeetCode

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

This problem is popular in LeetCode and GeeksForGeeks A collection of hundreds of interview questions and solutions are available in our blog at Interview Question Solutions
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SOLUTION:

Source code: Java

	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.Date;
	import java.util.HashMap;
	import java.util.List;
	import java.util.Map;
	/**
	* Given a digit string, return all possible letter combinations that the number could represent.
	A mapping of digit to letters (just like on the telephone buttons) is given below.
	Input:Digit string "23"
	Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
	*
	*/
	/**
	*
	* @author rbaral
	*
	*/
	public class LetterCombinationOfPhonenumber {
	public static void main(String[] args) {
	boolean testEnabled = true;
	if(testEnabled){
	performTest();
	}else{
	DateFormat format = new SimpleDateFormat("YYYY-M-d:H:m:s:S");
	System.out.println(format.format(new Date()));
	String digits="23";
	Object[] arrOutput = letterCombinations(digits).toArray();
	Arrays.sort(arrOutput);
	System.out.println("output is:"+Arrays.toString(arrOutput));
	System.out.println(format.format(new Date()));
	}
	}
	public static List<String> letterCombinations(String digits) {
	List<String> listOfStrings = new ArrayList<String>();
	List<String> tempList = new ArrayList<String>();
	String[] stringNum;
	for(int i=digits.length()-1;i>=0;i--){
	stringNum= getStringsForNumber(Integer.parseInt(String.valueOf(digits.charAt(i))));
	if(listOfStrings.isEmpty()){
	//just add the elements we got for the current number
	for(String s:stringNum){
	listOfStrings.add(s);
	}
	}else{
	//find the combination with every element of the lastPairs
	tempList.clear();
	for(int k=0; k<stringNum.length; k++){
	for(int l=0;l<listOfStrings.size();l++){
	tempList.add(stringNum[k]+listOfStrings.get(l));
	}
	}
	listOfStrings.clear();
	listOfStrings.addAll(tempList);
	}
	}
	return listOfStrings;
	}
	public static String[] getStringsForNumber(int num) {
	String[] value = new String[]{};
	switch (num) {
	case 2:
	value = new String[]{"a","b","c"};
	break;
	case 3:
	value = new String[]{"d","e","f"};
	break;
	case 4:
	value = new String[]{"g","h","i"};
	break;
	case 5:
	value = new String[]{"j","k","l"};
	break;
	case 6:
	value = new String[]{"m","n","o"};
	break;
	case 7:
	value = new String[]{"p","q","r","s"};
	break;
	case 8:
	value = new String[]{"t","u","v"};
	break;
	case 9:
	value = new String[]{"w","x","y","z"};
	break;
	default:
	value = new String[]{};
	}
	return value;
	}
	public static void performTest(){
	Map<String, List<String>> testCases= new HashMap<String, List<String>>();
	List<String> failedCases = new ArrayList<String>();
	List<String> result=new ArrayList<String>();
	List<String> a = new ArrayList<String>(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"));
	testCases.put("234", a);
	a= new ArrayList<String>(Arrays.asList("ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"));
	testCases.put("23", a);
	List<String> expected = new ArrayList<String>();
	for(String testCase: testCases.keySet()){
	result = letterCombinations(testCase);
	expected = testCases.get(testCase);
	for(String resItem:result){
	if(!expected.contains(resItem)){
	failedCases.add("Failed for:{"+testCase+"} got:"+Arrays.toString(result.toArray())+" expected:"+Arrays.toString(testCases.get(testCase).toArray()));
	break;
	}
	}
	}
	System.out.println("TEST RESULT, Passed:"+(testCases.size()-failedCases.size())+" failed:"+failedCases.size());
	for(String failure:failedCases)
	System.err.println(failure);
	}
	}

view raw LetterCombinationPhoneNumber.java hosted with ❤ by GitHub