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public boolean isThereCycle(Map<Character, List<Character>> map){
        if(map == null || map.isEmpty()) return false;

        //use each node as starting point
        for(char item : map.keySet()){
            //create new tracking experience for each start point
           Stack<Character> trackPad = new Stack<>();
           List<Character> visitedPoints = new ArrayList<>();

           visitedPoints.add(item);

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 //Keypad Number to Letter Mapping
 //2-9 corresponds to letters on the phone keypad and the same index of the array
    private static String[] keyPadMapping = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv" ,"wxyz"};
   
    public static List<String> playNumberLetterCombination(String number){

        List<String> combinedWords = new ArrayList<>();

        //empty or wrong input
        if(number.isEmpty() || !number.matches("\\d+")) return combinedWords;

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   public long getMinDifferenceInMinutes(String[] journal){
        if(journal == null) return 0;

        if(journal.length == 0) return 0;

        //Using a set to store unique and valid entries
        //if any entry is duplicated, it will auto break because that will be the minimum time difference
        //TreeSet stores data in natural order - O(Log N) time complexity - better than sorting array with NLogN
        //sorting keeps times close together and will eliminate comparing each entry with all other elements
        //Tradeoff extra space for faster sort process

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//-1 move student from front of line to back
//+1 move student from back of line to front
//0 no movement
public int[] shuffleLine(int[] line, int numberToShuffle){
        if(line == null) return new int[0];

        int lineLength = line.length;
        if(numberToShuffle == 0 || lineLength == 0 || Math.abs(numberToShuffle) == lineLength) return line;

        if(Math.abs(numberToShuffle) > lineLength)

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public int[] mergeSortedArray(int[] classA, int[] classB){
        if(classA == null && classB == null) return new int[0];
        else if (classA == null) return classB;
        else if (classB == null) return classA;

        int aIndex = 0, bIndex = 0, mergeIndex = 0, classLength = classA.length+classB.length;
        int[] merged = new int[classLength];

        while(mergeIndex < classLength){
            if(aIndex<classA.length && bIndex<classB.length){

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public int[] getProducts(int[] nums){

        if(nums == null) return new int[0];
        if(nums.length == 0) return new int[0];
        if(nums.length == 1) return new int[]{0};


        int[] products = new int[nums.length];

        //any number multiplied by 1 is the same number; therefore allProducts cannot be initialized to 0

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public int[] getBoundaryIndexesOfVal(int[] nums, int val){      
        if(nums == null) return new int[] {-1, -1};

        if (nums.length == 0) return new int[] {-1, -1};
        
        int startIndex = 0;
        int endIndex = nums.length - 1;

        //keep count of elements before and after the specified value
        int preValCount = 0;

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public int countOfElementsExcludingVal(int[] nums, int val){
        if(nums == null) return 0;

        int countWithoutVal = nums.length;

        for(int item : nums){

            if (item == val) countWithoutVal--;
        }
         return countWithoutVal;

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public int uniqueCountOfElements(int[] nums)
    {
        if (nums == null) return 0;
        
        int arrSize = nums.length;
        if (arrSize == 0) return 0;

        int finalCount = 1; // Count the first element by default
        for(int count = 0; count < arrSize; count++)
        {