Program to invert a tree

Author: mandliya

README.md

@@ -6,8 +6,8 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 138 |
-| Current Streak | 2 days |
+| Total Problems | 139 |
+| Current Streak | 3 days |
 | Longest Streak | 91 ( August 17, 2015 - November 15, 2015 ) |
 
 </center>
@@ -121,6 +121,7 @@ Include contains single header implementation of data structures and some algori
 | Given a binary tree and key, return the level of the node with key. Root is at level 1, and if node with key does not exists in tree, return 0| [level_of_node.cpp](tree_problems/level_of_node.cpp)|
 | Given a binary tree, find all the paths from root to nodes, whose sum is k. | [k_sum_paths.cpp](tree_problems/k_sum_paths.cpp)|
 | Given a binary tree, print its nodes level by level in reverse order. i.e. all nodes present at last level should be printed first followed by nodes of second-last level and so on.. All nodes for any level should be printed from left to right. | [reverseLevelOrderTraversal.cpp](tree_problems/reverseLevelOrderTraversal.cpp) |
+| Invert a binary tree, recursively and iteratively.| [invert_a_tree.cpp](tree_problems/invert_a_tree.cpp) |
 
 ### String Problems
 | Problem | Solution |

tree_problems/invert_a_tree.cpp

@@ -0,0 +1,117 @@
+/*
+ * Invert given Binary Tree | Recursive and Iterative solution
+ *                  1                         1
+ *              /       \                 /       \
+ *             2         3      ->       3         2
+ *           /   \     /   \           /   \     /   \
+ *          4     5   6     7         7     6   5     4
+ *
+ */
+
+#include <bits/stdc++.h>
+
+ struct TreeNode
+ {
+     int data;
+     TreeNode *left;
+     TreeNode *right;
+     TreeNode(int d)
+        : data{d}, left{nullptr}, right{nullptr} {}
+ };
+
+void invertTreeRecur(TreeNode* root)
+{
+    if (!root)
+    {
+        return;
+    }
+
+    // Swap left and right trees
+    //
+    TreeNode* temp = root->left;
+    root->left = root->right;
+    root->right = temp;
+
+    // Do this recursively for left and right sub-trees.
+    //
+    invertTreeRecur(root->left);
+    invertTreeRecur(root->right);
+}
+
+void invertTreeIter(TreeNode* root)
+{
+    if (!root)
+    {
+        return;
+    }
+    std::queue<TreeNode*> nodeQueue;
+    nodeQueue.push(root);
+    while(!nodeQueue.empty())
+    {
+        TreeNode* curr = nodeQueue.front();
+        nodeQueue.pop();
+
+        // Swap left and right children
+        //
+        TreeNode* temp = curr->left;
+        curr->left = curr->right;
+        curr->right = temp;
+
+        if (curr->left)
+        {
+            nodeQueue.push(curr->left);
+        }
+
+        if (curr->right)
+        {
+            nodeQueue.push(curr->right);
+        }
+    }
+}
+
+// Prints post order traversal of tree, where level expands left to right.
+//
+void postOrder(TreeNode* root, int indent = 0)
+{
+    if (root)
+    {
+        if(root->right)
+        {
+            postOrder(root->right, indent+4);
+        }
+        if (indent) {
+            std::cout << std::setw(indent) << ' ';
+        }
+        if (root->right)
+        {
+            std::cout<<" /\n" << std::setw(indent) << ' ';
+        }
+        std::cout<< root->data << "\n ";
+        if(root->left)
+        {
+            std::cout << std::setw(indent) << ' ' <<" \\\n";
+            postOrder(root->left, indent + 4);
+        }
+    }
+}
+
+ int main()
+ {
+    TreeNode *root = new TreeNode(1);
+    root->left = new TreeNode(2);
+    root->right = new TreeNode(3);
+    root->left->left = new TreeNode(4);
+    root->left->right = new TreeNode(5);
+    root->right->left = new TreeNode(6);
+    root->right->right = new TreeNode(7);
+    std::cout << "Current Tree: \n";
+    postOrder(root);
+    std::cout << "\nInverting it recursively:\n";
+    invertTreeRecur(root);
+    postOrder(root);
+    std::cout << "\nInverting it again iteratively:\n";
+    invertTreeIter(root);
+    postOrder(root);
+    std::cout << std::endl;
+    return 0;
+ }