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A simple example demonstrating the construction of binary trees.

Python, 120 lines
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# A binary ordered tree example

class CNode:
    left , right, data = None, None, 0
    
    def __init__(self, data):
        # initializes the data members
        self.left = None
        self.right = None
        self.data = data

class CBOrdTree:
    def __init__(self):
        # initializes the root member
        self.root = None
    
    def addNode(self, data):
        # creates a new node and returns it
        return CNode(data)

    def insert(self, root, data):
        # inserts a new data
        if root == None:
            # it there isn't any data
            # adds it and returns
            return self.addNode(data)
        else:
            # enters into the tree
            if data <= root.data:
                # if the data is less than the stored one
                # goes into the left-sub-tree
                root.left = self.insert(root.left, data)
            else:
                # processes the right-sub-tree
                root.right = self.insert(root.right, data)
            return root
        
    def lookup(self, root, target):
        # looks for a value into the tree
        if root == None:
            return 0
        else:
            # if it has found it...
            if target == root.data:
                return 1
            else:
                if target < root.data:
                    # left side
                    return self.lookup(root.left, target)
                else:
                    # right side
                    return self.lookup(root.right, target)
        
    def minValue(self, root):
        # goes down into the left
        # arm and returns the last value
        while(root.left != None):
            root = root.left
        return root.data

    def maxDepth(self, root):
        if root == None:
            return 0
        else:
            # computes the two depths
            ldepth = self.maxDepth(root.left)
            rdepth = self.maxDepth(root.right)
            # returns the appropriate depth
            return max(ldepth, rdepth) + 1
            
    def size(self, root):
        if root == None:
            return 0
        else:
            return self.size(root.left) + 1 + self.size(root.right)

    def printTree(self, root):
        # prints the tree path
        if root == None:
            pass
        else:
            self.printTree(root.left)
            print root.data,
            self.printTree(root.right)

    def printRevTree(self, root):
        # prints the tree path in reverse
        # order
        if root == None:
            pass
        else:
            self.printRevTree(root.right)
            print root.data,
            self.printRevTree(root.left)

if __name__ == "__main__":
    # create the binary tree
    BTree = CBOrdTree()
    # add the root node
    root = BTree.addNode(0)
    # ask the user to insert values
    for i in range(0, 5):
        data = int(raw_input("insert the node value nr %d: " % i))
        # insert values
        BTree.insert(root, data)
    print
    
    BTree.printTree(root)
    print
    BTree.printRevTree(root)
    print
    data = int(raw_input("insert a value to find: "))
    if BTree.lookup(root, data):
        print "found"
    else:
        print "not found"
        
    print BTree.minValue(root)
    print BTree.maxDepth(root)
    print BTree.size(root)

It's a toy example written years ago to implement a binary tree in Python. Useful for newbies or for a base for something else

4 comments

Rodrigo Senra 17 years, 4 months ago  # | flag

Small suggestion. Nice example. IMHO you should just change the B-Tree comment to binary tree, although this code can hold multiple info per node, it does not implement a B-Tree structure neither has its properties (like being balanced, having a maximum number of buckets per node and short in height).

Foo Bear (author) 17 years, 4 months ago  # | flag

Fixed. thanks :)

Vicente Soler 11 years, 11 months ago  # | flag

I can see, by running the example, that zero (0) is always a node. Can we get rid of it? How could it be done?

Why cannt feed letters (or texts) into the binary tree?

Thank you

Grant Jenks 7 years, 2 months ago  # | flag

If you're looking for an API similar to that provided by a binary search tree, check out the sortedcontainers module. It implements sorted list, sorted dict, and sorted set data types in pure-Python and is fast-as-C implementations (even faster!). Learn more about sortedcontainers, available on PyPI and github.

Created by Foo Bear on Tue, 13 Jul 2004 (PSF)
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