posted original 2-3_tree Python code

Author: joeyajames

2-3_tree.py

@@ -0,0 +1,146 @@
+# 2-3 Tree
+# balanced tree data structure with up to 2 data items per node
+
+class Node:
+	def __init__(self, data, par = None):
+		#print ("Node __init__: " + str(data))
+		self.data = list([data])
+		self.parent = par
+		self.child = list()
+		
+	def __str__(self):
+		if self.parent:
+			return str(self.parent.data) + ' : ' + str(self.data)
+		return 'Root : ' + str(self.data)
+	
+	def __lt__(self, node):
+		return self.data[0] < node.data[0]
+		
+	def _isLeaf(self):
+		return len(self.child) == 0
+			
+	# merge new_node sub-tree into self node
+	def _add(self, new_node):
+		# print ("Node _add: " + str(new_node.data) + ' to ' + str(self.data))
+		for child in new_node.child:
+			child.parent = self
+		self.data.extend(new_node.data)
+		self.data.sort()
+		self.child.extend(new_node.child)
+		if len(self.child) > 1:
+			self.child.sort()
+			for child in self.child:
+				child.parent = self
+		if len(self.data) > 2:
+			self._split()
+	
+	# find correct node to insert new node into tree
+	def _insert(self, new_node):
+		# print ('Node _insert: ' + str(new_node.data) + ' into ' + str(self.data))
+		
+		# leaf node - add data to leaf and rebalance tree
+		if self._isLeaf():
+			self._add(new_node)
+			
+		# not leaf - find correct child to descend, and do recursive insert
+		elif new_node.data[0] > self.data[-1]:
+			self.child[-1]._insert(new_node)
+		else:
+			for i in range(0, len(self.data)):
+				if new_node.data[0] < self.data[i]:
+					self.child[i]._insert(new_node)
+					break
+	
+	# 3 items in node, split into new sub-tree and add to parent	
+	def _split(self):
+		# print("Node _split: " + str(self.data))
+		left_child = Node(self.data[0], self)
+		right_child = Node(self.data[2], self)
+		if self.child:
+			self.child[0].parent = left_child
+			self.child[1].parent = left_child
+			self.child[2].parent = right_child
+			self.child[3].parent = right_child
+			left_child.child = [self.child[0], self.child[1]]
+			right_child.child = [self.child[2], self.child[3]]
+					
+		self.child = [left_child]
+		self.child.append(right_child)
+		self.data = [self.data[1]]
+		
+		# now have new sub-tree, self. need to add self to its parent node
+		if self.parent:
+			if self in self.parent.child:
+				self.parent.child.remove(self)
+			self.parent._add(self)
+		else:
+			left_child.parent = self
+			right_child.parent = self
+			
+	# find an item in the tree; return item, or False if not found		
+	def _find(self, item):
+		# print ("Find " + str(item))
+		if item in self.data:
+			return item
+		elif self._isLeaf():
+			return False
+		elif item > self.data[-1]:
+			return self.child[-1]._find(item)
+		else:
+			for i in range(len(self.data)):
+				if item < self.data[i]:
+					return self.child[i]._find(item)
+		
+	def _remove(self, item):
+		pass
+		
+	# print preorder traversal		
+	def _preorder(self):
+		print (self) 
+		for child in self.child:
+			child._preorder()
+	
+class Tree:
+	def __init__(self):
+		print("Tree __init__")
+		self.root = None
+		
+	def insert(self, item):
+		print("Tree insert: " + str(item))
+		if self.root is None:
+			self.root = Node(item)
+		else:
+			self.root._insert(Node(item))
+			while self.root.parent:
+				self.root = self.root.parent
+		return True
+	
+	def find(self, item):
+		return self.root._find(item)
+		
+	def remove(self, item):
+		self.root.remove(item)
+		
+	def printTop2Tiers(self):
+		print ('----Top 2 Tiers----')
+		print (str(self.root.data))
+		for child in self.root.child:
+			print (str(child.data), end=' ')
+		print(' ')
+		
+	def preorder(self):
+		print ('----Preorder----')
+		self.root._preorder()
+		
+tree = Tree()
+
+lst = [13, 7, 24, 15, 4, 29, 20, 16, 19, 1, 5, 22, 17]
+for item in lst:
+	tree.insert(item)
+tree.printTop2Tiers()
+
+# for i in range (25):
+	# tree.insert(i)
+	# tree.printTop2Tiers()
+# tree.preorder()
+# print (tree.find(16))