Day5: Zig zag tree traversal python

Author: mandliya

README.md

@@ -7,10 +7,10 @@
 | Current Status|     Stats     |
 | :------------: | :----------: |
 | Total C++ Problems | 188 |
-| Total Python Problems | 9 |
-| Current Daily Streak| 4 |
+| Total Python Problems | 10 |
+| Current Daily Streak| 5 |
 | Last Streak | 06/20/2019 - 06/21/2019|
-| Current Streak | 06/23/2019 - 06/26/2019|
+| Current Streak | 06/23/2019 - 06/27/2019|
 
 </center>
 
@@ -117,7 +117,7 @@ Include contains single header implementation of data structures and some algori
 | :------------ | :----------: |
 |Iterative Level order traversal of Tree using queue |[levelOrderTraversalIterative.cpp](tree_problems/levelOrderTraversalIterative.cpp), [level_order_tree_traversal_iterative.py](tree_problems/level_order_tree_traversal_iterative.py)|
 |Recursive Level order traveral of Tree | [levelOrderTraversalRecursive.cpp](tree_problems/levelOrderTraversalRecursive.cpp), [level_order_tree_traversal_recursive.py](tree_problems/level_order_tree_traversal_recursive.py)|
-|ZigZag Traversal of Tree | [zigZagTraversal.cpp](tree_problems/zigZagTraversal.cpp)|
+|ZigZag Traversal of Tree | [zigZagTraversal.cpp](tree_problems/zigZagTraversal.cpp), [zig_zag_traversal.py](tree_problems/zig_zag_traversal.py)|
 |Predecessor and Successor of a given node in Binary Search Tree | [predecessorSuccessor.cpp](tree_problems/predecessorSuccessor.cpp)|
 |Given values of two nodes in a Binary Search Tree, find the Lowest Common Ancestor (LCA). Assume that both the values exist in the tree.| [lowest-common-ancestor.cpp](tree_problems/lowest-common-ancestor.cpp)|
 |Given a binary tree (unlike binary search tree), find the Lowest Common Ancestor (LCA).|[lowest-common-ancestor-binary-tree.cpp](tree_problems/lowest-common-ancestor-binary-tree.cpp)|

tree_problems/zig_zag_traversal.py

@@ -0,0 +1,89 @@
+
+# Given a binary Tree
+# 		    1
+# 		 /     \
+# 	     2	     3
+# 	    / \ 	/ \
+#  	   4  5    6   7
+# Print zig-zag level order traversal
+# 1 3 2 4 5 6 7
+#
+
+class TreeNode:
+    def __init__(self, data):
+        """Representation of a binary tree node"""
+        self.data = data
+        self.left = None
+        self.right = None
+
+
+class Tree:
+    def __init__(self):
+        """Reprentation of a binary tree"""
+        self.root = None
+
+    def _print_level(self, node, level, zig):
+        """Utility function to print the level, level starts with 1"""
+        if node is None:
+            return
+        if level == 1:
+            print(node.data, end=' ')
+            return
+        else:
+            if zig:
+                self._print_level(node.left, level-1, zig)
+                self._print_level(node.right, level-1, zig)
+            else:
+                self._print_level(node.right, level-1, zig)
+                self._print_level(node.left, level-1, zig)
+
+    def _height(self, node):
+        """Gets the height of the tree from node"""
+        if node is None:
+            return 0
+        else:
+            return max(self._height(node.left), self._height(node.right)) + 1
+
+    def print_zig_zag(self):
+        """Prints the zig zag level order"""
+        if self.root is None:
+            return
+        h = self._height(self.root)
+        zig = True
+        for i in range(1, h+1):
+            self._print_level(self.root, i, not zig)
+            print()
+    
+    def in_order(self):
+        """In order traversal of the tree"""
+        current = self.root
+        stack = []
+        done = False
+        while not done:
+            if current is not None:
+                stack.append(current)
+                current = current.left
+
+            elif stack:
+                current = stack.pop()
+                print(current.data, end=' ')
+                current = current.right
+            else:
+                done = True
+        print()
+
+if __name__ == "__main__":
+    tree = Tree()
+    tree.root = TreeNode(1)
+    tree.root.left = TreeNode(2)
+    tree.root.right = TreeNode(3)
+    tree.root.left.left = TreeNode(4)
+    tree.root.left.right = TreeNode(5)
+    tree.root.right.left = TreeNode(6)
+    tree.root.right.right = TreeNode(7)
+
+    print("In order:")
+    tree.in_order()
+
+    print("Zig zag level order:")
+    tree.print_zig_zag()