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# graph is represented by adjacency list: List[List[int]]
# s: start vertex
def dfs_iterating(graph, s):
    # set is used to mark visited vertices
    visited = set()

    # create a stack for DFS
    stack = []

    # Push vertex s to the stack

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# graph is represented by adjacency list: List[List[int]]
# s: start vertex
def dfs(graph, s):
    # set is used to mark visited vertices
    visited = set()

    def recur(current_vertex):
        print(current_vertex)

        # mark it visited

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from collections import deque

# graph: List[List[int]]
# s: start vertex
def bfs(graph, s):
    # set is used to mark visited vertices
    visited = set()

    # create a queue for BFS 
    queue = deque()

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class TrieNode(object):

    def __init__(self):
        self.children = {}
        self.is_word = False    # mark the end of a word


class Trie(object):

    def __init__(self):

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from collections import deque

def levelorder_traversal_iterating(root):
    if not root:
        return []

    result = []
    # using queue
    queue = deque([root])
    while queue:

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None

def levelorder_traversal_recursive(root):
    result = []

    def recur(node, level):

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def postorder_traversal_iterating(root):
    if not root:
        return []

    result = []
    stack = [root]
    # get the result in order of node, right, left
    while stack:
        current = stack.pop()
        if current.left:

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None

def postorder_traversal_recursive(root):
    result = []

    def recur(node):

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def preorder_traversal_iterating(root):
    if not root:
        return []
    
    result = []
    # using stack
    stack = [root]
    while stack:
        current = stack.pop()
        # visit node

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None

def preorder_traversal_recursive(root):
    result = []

    def recur(node):