Adding function for actual level order traversal (#699)

traversals/binary_tree_traversals.py

@@ -2,10 +2,11 @@
 This is pure python implementation of tree traversal algorithms
 """
 from __future__ import print_function
+
 import queue
 
 try:
-    raw_input          # Python 2
+    raw_input  # Python 2
 except NameError:
     raw_input = input  # Python 3
 
@@ -22,7 +23,7 @@ def build_tree():
     print("Enter the value of the root node: ", end="")
     check = raw_input().strip().lower()
     if check == 'n':
-        return None 
+        return None
     data = int(check)
     q = queue.Queue()
     tree_node = TreeNode(data)
@@ -46,6 +47,7 @@ def build_tree():
         node_found.right = right_node
         q.put(right_node)
 
+
 def pre_order(node):
     if not isinstance(node, TreeNode) or not node:
         return
@@ -53,6 +55,7 @@ def pre_order(node):
     pre_order(node.left)
     pre_order(node.right)
 
+
 def in_order(node):
     if not isinstance(node, TreeNode) or not node:
         return
@@ -82,22 +85,43 @@ def level_order(node):
         if node_dequeued.right:
             q.put(node_dequeued.right)
 
-#iteration version
+
+def level_order_actual(node):
+    if not isinstance(node, TreeNode) or not node:
+        return
+    q = queue.Queue()
+    q.put(node)
+    while not q.empty():
+        list = []
+        while not q.empty():
+            node_dequeued = q.get()
+            print(node_dequeued.data, end=" ")
+            if node_dequeued.left:
+                list.append(node_dequeued.left)
+            if node_dequeued.right:
+                list.append(node_dequeued.right)
+        print()
+        for node in list:
+            q.put(node)
+
+
+# iteration version
 def pre_order_iter(node):
     if not isinstance(node, TreeNode) or not node:
         return
     stack = []
     n = node
     while n or stack:
-        while n:    #start from root node, find its left child
+        while n:  # start from root node, find its left child
             print(n.data, end=" ")
             stack.append(n)
             n = n.left
-        #end of while means current node doesn't have left child
+        # end of while means current node doesn't have left child
         n = stack.pop()
-        #start to traverse its right child
+        # start to traverse its right child
         n = n.right
 
+
 def in_order_iter(node):
     if not isinstance(node, TreeNode) or not node:
         return
@@ -111,22 +135,24 @@ def in_order_iter(node):
         print(n.data, end=" ")
         n = n.right
 
+
 def post_order_iter(node):
     if not isinstance(node, TreeNode) or not node:
         return
     stack1, stack2 = [], []
     n = node
     stack1.append(n)
-    while stack1:   #to find the reversed order of post order, store it in stack2
+    while stack1:  # to find the reversed order of post order, store it in stack2
         n = stack1.pop()
         if n.left:
             stack1.append(n.left)
         if n.right:
             stack1.append(n.right)
         stack2.append(n)
-    while stack2:   #pop up from stack2 will be the post order
+    while stack2:  # pop up from stack2 will be the post order
         print(stack2.pop().data, end=" ")
 
+
 if __name__ == '__main__':
     print("\n********* Binary Tree Traversals ************\n")
 
@@ -147,6 +173,10 @@ if __name__ == '__main__':
     level_order(node)
     print("\n******************************************\n")
 
+    print("\n********* Actual Level Order Traversal ************")
+    level_order_actual(node)
+    print("\n******************************************\n")
+
     print("\n********* Pre Order Traversal - Iteration Version ************")
     pre_order_iter(node)
     print("\n******************************************\n")
@@ -157,4 +187,4 @@ if __name__ == '__main__':
 
     print("\n********* Post Order Traversal - Iteration Version ************")
     post_order_iter(node)
-    print("\n******************************************\n")
+    print("\n******************************************\n")