Merge pull request kothariji#583 from Bikash0007/patch-3

Foldable Binary Trees

Author: kothariji

Tree/foldable_btree.cpp

@@ -0,0 +1,121 @@
+#include <bits/stdc++.h>
+using namespace std;
+ 
+/* You would want to remove below
+3 lines if your compiler supports
+bool, true and false */
+#define bool int
+#define true 1
+#define false 0
+ 
+/* A binary tree node has data,
+pointer to left child and a
+pointer to right child */
+class node {
+public:
+    int data;
+    node* left;
+    node* right;
+};
+ 
+/* converts a tree to its mirror image */
+void mirror(node* node);
+ 
+/* returns true if structure of
+two trees a and b is same only
+structure is considered for comparison, not data! */
+bool isStructSame(node* a, node* b);
+ 
+/* Returns true if the given tree is foldable */
+bool isFoldable(node* root)
+{
+    bool res;
+ 
+    /* base case */
+    if (root == NULL)
+        return true;
+ 
+    /* convert left subtree to its mirror */
+    mirror(root->left);
+ 
+    /* Compare the structures of the
+    right subtree and mirrored
+    left subtree */
+    res = isStructSame(root->left, root->right);
+ 
+    /* Get the original tree back */
+    mirror(root->left);
+ 
+    return res;
+}
+ 
+bool isStructSame(node* a, node* b)
+{
+    if (a == NULL && b == NULL) {
+        return true;
+    }
+    if (a != NULL && b != NULL && isStructSame(a->left, b->left) && isStructSame(a->right, b->right)) {
+        return true;
+    }
+ 
+    return false;
+}
+ 
+/* UTILITY FUNCTIONS */
+/* Change a tree so that the roles of the left and
+    right pointers are swapped at every node.
+    See https:// www.geeksforgeeks.org/?p=662 for details */
+void mirror(node* Node)
+{
+    if (Node == NULL)
+        return;
+    else {
+        node* temp;
+ 
+        /* do the subtrees */
+        mirror(Node->left);
+        mirror(Node->right);
+ 
+        /* swap the pointers in this node */
+        temp = Node->left;
+        Node->left = Node->right;
+        Node->right = temp;
+    }
+}
+ 
+/* Helper function that allocates a new node with the
+given data and NULL left and right pointers. */
+node* newNode(int data)
+{
+    node* Node = new node();
+    Node->data = data;
+    Node->left = NULL;
+    Node->right = NULL;
+ 
+    return (Node);
+}
+ 
+/* Driver program to test mirror() */
+int main(void)
+{
+    /* The constructed binary tree is
+            1
+        / \
+        2 3
+        \ /
+        4 5
+    */
+    node* root = newNode(1);
+    root->left = newNode(2);
+    root->right = newNode(3);
+    root->right->left = newNode(4);
+    root->left->right = newNode(5);
+ 
+    if (isFoldable(root) == 1) {
+        cout << "tree is foldable";
+    }
+    else {
+        cout << "\ntree is not foldable";
+    }
+    return 0;
+}