Problem:
Binary Search Tree II Write a program which performs the following operations to a binary search tree $T$ by adding the find operation to A: Binary Search Tree I.  insert $k$: Insert a node containing $k$ as key into $T$.  find $k$: Report whether $T$ has a node containing $k$.  print : Print the keys of the binary search tree by inorder tree walk and  preorder tree walk respectively.  Input In the first line, the number of operations $m$ is given. In the following $m$ lines, operations represented by insert $k$, find $k$ or print are given. Output For each find $k$ operation, print " yes " if $T$ has a node containing $k$, " no " if not. In addition, for each print operation, print a list of keys obtained by inorder tree walk and preorder tree walk in a line respectively. Put a space character before each key . Constraints  The number of operations $\leq 500,000$  The number of print operations $\leq 10$.  $-2,000,000,000 \leq key \leq 2,000,000,000$  The height of the binary tree does not exceed 100 if you employ the above pseudo code.  The keys in the binary search tree are all different.  Sample Input 1 10
insert 30
insert 88
insert 12
insert 1
insert 20
find 12
insert 17
insert 25
find 16
print Sample Output 1 yes
no
 1 12 17 20 25 30 88
 30 12 1 20 17 25 88 Reference Introduction to Algorithms, Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein. The MIT Press.

Solution (Python):
class Node:
    def __init__(self, key, parent=None, left=None, right=None):
        self.key = key
        self.parent = parent
        self.left = left
        self.right = right


root = None

def insert(k):
    global root
    y = None
    x = root
    z = Node(k)

    while x is not None:
        y = x
        if z.key < x.key:
            x = x.left
        else:
            x = x.right

    z.parent = y
    if y is None:
        root = z
    else:
        if z.key < y.key:
            y.left = z
        else:
            y.right = z


def find(u, k):
    while u is not None and k != u.key:
        if k < u.key:
            u = u.left
        else:
            u = u.right
    return u


def inorder(u):
    if u is None:
        return
    inorder(u.left)
    print(' %d' % u.key, end='')
    inorder(u.right)


def preorder(u):
    if u is None:
        return
    print(' %d' % u.key, end='')
    preorder(u.left)
    preorder(u.right)


n = int(input())
for i in range(n):
    cmd = input().split()
    if cmd[0] == 'insert':
        insert(int(cmd[1]))
    elif cmd[0] == 'find':
        if find(root, int(cmd[1])) is not None:
            print('yes')
        else:
            print('no')
    elif cmd[0] == 'print':
        inorder(root)
        print()
        preorder(root)
        print()

Solution (Python):
class Node:
	def __init__(self, key):
		self.key = key
		self.left = self.right = self.parent = None

class BST:
	def __init__(self):
		self.root = None
	
	def insert(self, key):
		parent = None
		current = self.root
		while current != None:
			parent = current
			if key < current.key:
				current = current.left
			else:
				current = current.right
		new = Node(key)
		new.parent = parent
		if parent == None:
			self.root = new
		elif key < parent.key:
			parent.left = new
		else:
			parent.right = new		
	
	def find(self, key):
		current = self.root
		while current != None:
			if key == current.key:
				return current
			if key < current.key:
				current = current.left
			else:
				current = current.right
		return None
		
	def delete(self, key):
		return
	
	def print(self):
		self.print_in_order(self.root)
		print()
		self.print_pre_order(self.root)
		print()
		
	def print_in_order(self, node):
		if node != None:
			self.print_in_order(node.left)
			print(' ' + str(node.key), end='')
			self.print_in_order(node.right)
		
	def print_pre_order(self, node):
		if node != None:
			print(' ' + str(node.key), end='')
			self.print_pre_order(node.left)
			self.print_pre_order(node.right)		

n = int(input())
bst = BST()
for i in range(n):
	cmd = list(map(str, input().split()))
	if cmd[0] == 'print':
		bst.print()
	else:
		key = int(cmd[1])
		if cmd[0] == 'insert':
			bst.insert(key)
		elif cmd[0] == 'find':
			if bst.find(key) != None:
				print('yes')
			else:
				print('no')
		else:
			bst.delete(key)

Solution (Python):

class Tree:
    def __init__(self):
        self.root = None
        self.size = 0
    
    def find(self, key):
        return self._find(key, self.root)

    def _find(self, key, nd):
        if not nd: return False
        if nd.key == key: return True
        if key < nd.key:
            return self._find(key, nd.left)
        else:
            return self._find(key, nd.right)
    
    def printorder(self):
        self._preorder_walk(self.root)
        print()
        self._inorder_walk(self.root)
        print()

    def _inorder_walk(self, nd):
        print(' {0}'.format(nd.key), end='')
        if nd.left: self._inorder_walk(nd.left)
        if nd.right: self._inorder_walk(nd.right)

    def _preorder_walk(self, nd):
        if nd.left: self._preorder_walk(nd.left)
        print(' {0}'.format(nd.key), end='')
        if nd.right: self._preorder_walk(nd.right)

class Node:
    def num_child(self):
        d = 1 if self.left else 0
        d += 1 if self.right else 0
        return d
    def __init__(self, key):
        self.key = key
        self.right,self.left = None,None
        self.parent = None
    def __str__(self):
        return 'node key: ' + str(self.key)

def insert(T, z):
    y = None
    x = T.root
    while not x == None:
        y = x
        if z.key < x.key:
            x = x.left
        else:
            x = x.right
    z.parent = y
    if z.parent == None:
        T.root = z
    elif z.key < y.key:
        y.left = z
    else:
        y.right = z
    T.size += 1

m = int(input())
T = Tree()
for _ in range(m):
    ss = input().split()
    op = ss[0]
    if op == 'insert':
        v = int(ss[1])
        insert(T, Node(v))
    elif op == 'print':
        T.printorder()
    elif op == 'find':
        v = int(ss[1])
        if T.find(v): print('yes')
        else: print('no')