add binary_tree_traversals.py to data_structures (TheAlgorithms#3297)

* add binary_tree_traversals.py to data_structures

I have added some interesting binary tree traversing methods.

* Fixed error

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update binary_tree_traversals.py

* Update binary_tree_traversals.py

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update binary_tree_traversals.py

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update binary_tree_traversals.py

* Doctests and type hints

* Add spaces

* Update binary_tree_traversals.py

* black exclude data_structures/binary_tree/binary_tree_traversals.py

* Add spaces again

* Update binary_tree_traversals.py

Co-authored-by: Christian Clauss <cclauss@me.com>

.pre-commit-config.yaml

@@ -18,6 +18,10 @@ repos:
     rev: stable
     hooks:
       - id: black
+    exclude: |
+      (?x)^(
+        data_structures/binary_tree/binary_tree_traversals.py
+      )$
   - repo: https://github.com/PyCQA/isort
     rev: 5.5.3
     hooks:

data_structures/binary_tree/binary_tree_traversals.py

@@ -0,0 +1,161 @@
+# https://en.wikipedia.org/wiki/Tree_traversal
+
+
+class Node:
+    """
+    A Node has data variable and pointers to its left and right nodes.
+    """
+
+    def __init__(self, data):
+        self.left = None
+        self.right = None
+        self.data = data
+
+
+def make_tree() -> Node:
+    root = Node(1)
+    root.left = Node(2)
+    root.right = Node(3)
+    root.left.left = Node(4)
+    root.left.right = Node(5)
+    return root
+
+
+def preorder(root: Node):
+    """
+    Pre-order traversal visits root node, left subtree, right subtree.
+    >>> preorder(make_tree())
+    [1, 2, 4, 5, 3]
+    """
+    return [root.data] + preorder(root.left) + preorder(root.right) if root else []
+
+
+def postorder(root: Node):
+    """
+    Post-order traversal visits left subtree, right subtree, root node.
+    >>> postorder(make_tree())
+    [4, 5, 2, 3, 1]
+    """
+    return postorder(root.left) + postorder(root.right) + [root.data] if root else []
+
+
+def inorder(root: Node):
+    """
+    In-order traversal visits left subtree, root node, right subtree.
+    >>> inorder(make_tree())
+    [4, 2, 5, 1, 3]
+    """
+    return inorder(root.left) + [root.data] + inorder(root.right) if root else []
+
+
+def height(root: Node):
+    """
+    Recursive function for calculating the height of the binary tree.
+    >>> height(None)
+    0
+    >>> height(make_tree())
+    3
+    """
+    return (max(height(root.left), height(root.right)) + 1) if root else 0
+
+
+def level_order_1(root: Node):
+    """
+    Print whole binary tree in Level Order Traverse.
+    Level Order traverse: Visit nodes of the tree level-by-level.
+    """
+    if not root:
+        return
+    temp = root
+    que = [temp]
+    while len(que) > 0:
+        print(que[0].data, end=" ")
+        temp = que.pop(0)
+        if temp.left:
+            que.append(temp.left)
+        if temp.right:
+            que.append(temp.right)
+    return que
+
+
+def level_order_2(root: Node, level: int):
+    """
+    Level-wise traversal: Print all nodes present at the given level of the binary tree
+    """
+    if not root:
+        return root
+    if level == 1:
+        print(root.data, end=" ")
+    elif level > 1:
+        level_order_2(root.left, level - 1)
+        level_order_2(root.right, level - 1)
+
+
+def print_left_to_right(root: Node, level: int):
+    """
+    Print elements on particular level from left to right direction of the binary tree.
+    """
+    if not root:
+        return
+    if level == 1:
+        print(root.data, end=" ")
+    elif level > 1:
+        print_left_to_right(root.left, level - 1)
+        print_left_to_right(root.right, level - 1)
+
+
+def print_right_to_left(root: Node, level: int):
+    """
+    Print elements on particular level from right to left direction of the binary tree.
+    """
+    if not root:
+        return
+    if level == 1:
+        print(root.data, end=" ")
+    elif level > 1:
+        print_right_to_left(root.right, level - 1)
+        print_right_to_left(root.left, level - 1)
+
+
+def zigzag(root: Node):
+    """
+    ZigZag traverse: Print node left to right and right to left, alternatively.
+    """
+    flag = 0
+    height_tree = height(root)
+    for h in range(1, height_tree + 1):
+        if flag == 0:
+            print_left_to_right(root, h)
+            flag = 1
+        else:
+            print_right_to_left(root, h)
+            flag = 0
+
+
+def main():  # Main function for testing.
+    """
+    Create binary tree.
+    """
+    root = make_tree()
+    """
+    All Traversals of the binary are as follows:
+    """
+    print(f"  In-order Traversal is {inorder(root)}")
+    print(f" Pre-order Traversal is {preorder(root)}")
+    print(f"Post-order Traversal is {postorder(root)}")
+    print(f"Height of Tree is {height(root)}")
+    print("Complete Level Order Traversal is : ")
+    level_order_1(root)
+    print("\nLevel-wise order Traversal is : ")
+    for h in range(1, height(root) + 1):
+        level_order_2(root, h)
+    print("\nZigZag order Traversal is : ")
+    zigzag(root)
+    print()
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    main()