Create Reverse_alternate.py

Reverse_alternate.py

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+MAX = 100
+
+# A Binary Tree node
+class Node:
+
+    def __init__(self, data):
+
+        self.left = None
+        self.right = None
+        self.data = data
+
+# A utility function to 
+# create a new Binary Tree
+# Node
+def newNode(item):
+
+    temp = Node(item)
+    return temp
+
+# Function to store nodes of 
+# alternate levels in an array
+def storeAlternate(root, arr, 
+                   index, l):
+
+    # Base case
+    if (root == None):
+        return index;
+
+    # Store elements of 
+    # left subtree
+    index = storeAlternate(root.left, 
+                           arr, index,
+                           l + 1);
+
+    # Store this node only if 
+    # this is a odd level node
+    if(l % 2 != 0):    
+        arr[index] = root.data;
+        index += 1;    
+
+    # Store elements of right 
+    # subtree
+    index=storeAlternate(root.right, 
+                         arr, index, 
+                         l + 1);
+    return index
+
+# Function to modify Binary Tree 
+# (All odd level nodes are
+# updated by taking elements from 
+# array in inorder fashion)
+def modifyTree(root, arr, index, l):
+
+    # Base case
+    if (root == None):
+        return index;
+
+    # Update nodes in left subtree
+    index=modifyTree(root.left, 
+                     arr, index, 
+                     l + 1);
+
+    # Update this node only 
+    # if this is an odd level 
+    # node
+    if (l % 2 != 0):    
+        root.data = arr[index];
+        index += 1;    
+
+    # Update nodes in right 
+    # subtree
+    index=modifyTree(root.right,
+                     arr, index, 
+                     l + 1);
+    return index
+
+# A utility function to 
+# reverse an array from 
+# index 0 to n-1
+def reverse(arr, n):
+
+    l = 0
+    r = n - 1;
+
+    while (l < r):        
+        arr[l], arr[r] = (arr[r], 
+                          arr[l]);        
+        l += 1
+        r -= 1
+
+# The main function to reverse 
+# alternate nodes of a binary tree
+def reverseAlternate(root):
+
+    # Create an auxiliary array 
+    # to store nodes of alternate 
+    # levels
+    arr = [0 for i in range(MAX)]
+    index = 0;
+
+    # First store nodes of 
+    # alternate levels
+    index=storeAlternate(root, arr, 
+                         index, 0);
+
+    # Reverse the array
+    reverse(arr, index);
+
+    # Update tree by taking 
+    # elements from array
+    index = 0;
+    index=modifyTree(root, arr, 
+                     index, 0);
+
+# A utility function to print
+# indorder traversal of a
+# binary tree
+def printInorder(root):
+
+    if(root == None):
+        return;
+    printInorder(root.left);
+    print(root.data, end = ' ')
+    printInorder(root.right);
+
+# Driver code
+if __name__=="__main__":
+
+    root = newNode('a');
+    root.left = newNode('b');
+    root.right = newNode('c');
+    root.left.left = newNode('d');
+    root.left.right = newNode('e');
+    root.right.left = newNode('f');
+    root.right.right = newNode('g');
+    root.left.left.left = newNode('h');
+    root.left.left.right = newNode('i');
+    root.left.right.left = newNode('j');
+    root.left.right.right = newNode('k');
+    root.right.left.left = newNode('l');
+    root.right.left.right = newNode('m');
+    root.right.right.left = newNode('n');
+    root.right.right.right = newNode('o');
+
+    print("Inorder Traversal of given tree")
+    printInorder(root);
+
+    reverseAlternate(root);
+
+    print("\nInorder Traversal of modified tree")
+    printInorder(root);