wohhie

public boolean canJump(int[] nums) {
  int len = nums.length - 1;
  int reachableIndex = len;
  
  for (int i = len; i >= 0; --i) {
      if (i + nums[i] >= reachableIndex) {
          reachableIndex = i;
      }
  }
  

wohhie

private int sum_tree_data(Node node){
    int x, y;
    if (node != null){
        x = sum_tree_data(node.left);
        y = sum_tree_data(node.right);
        return x + y + node.data;
    }

    return 0;
}

wohhie

private int treeHeight(Node node){
    int x, y;
    if (node != null){
        x = treeHeight(node.left);
        y = treeHeight(node.right);

        return (x > y) ?  x + 1 : y + 1;
    }
    return 0;
}

wohhie

private int count_who_have_both_children(Node node){
    int x, y;
    if (node != null){
        x = count_who_have_both_children(node.left);
        y = count_who_have_both_children(node.right);
        if (node.left != null && node.right != null){
            return x + y + 1;
        }else {
            return x + y;
        }

wohhie

private int count(Node node){
    int x, y;
    if (node != null){
        x = count(node.left);
        y = count(node.right);
        return x + y +1;
    }

    return 0;
}

wohhie

private void levelOrder(Node node){
    // 1. print the root data
    // 2. insert root address in queue
    // 3. while queue is not empty
    //      a. get the address of the queue
    //      check left child has data
    //          i. print the left child data
    //          j. insert data of left child
    //      else check right child has data
    //          i. print the right child data

wohhie

private void iterativeInOrder(Node node){
        // we are going to the left most item
        if (node == null) return;
        // create an empty stack and push root to it.
        Stack<Node> stack = new Stack<>();

        while (node != null || !stack.isEmpty()){
            // 1. inOrder(left_child)   // put the data into stack
            // 2. Print(node.data)
            // 3. inOrder(right_child)

wohhie

private void iterativePreOrder(Node node) {
        if (node == null) return;
        // create an empty stack and push root to it
        Stack<Node> stack = new Stack<>();

        while (node != null || !stack.isEmpty()){
            if (node != null){
                System.out.print(node.data + " ");
                stack.push(node);
                node = node.left;

wohhie

public int findKthLargestNumber(int[] arr, int k) {
    Queue<Integer> queue = new PriorityQueue<>((n1, n2) -> n1.compareTo(n2));
    for(int n : arr){
        queue.add(n);
        if (queue.size() > k){
            queue.poll();
        }
    }
    return queue.poll();
}

wohhie

/**
     * Calculate two value sum if the list is unsorted
     * ==========================================================
     * @param arr
     * @param target
     */
public List<List<Integer>> sum_Three_HashMap_unSorted(int[] arr, int target){
    Set<List<Integer>> result = new HashSet<>();
    Set<Integer> dups = new HashSet<>();
    Map<Integer, Integer> visited = new HashMap<>();