Split a BST into two balanced BSTs based on a value K
Given a Binary Search tree and an integer K, we have to split the tree into two Balanced Binary Search Tree, where BST-1 consists of all the nodes which are less than K and BST-2 consists of all the nodes which are greater than or equal to K.
Note: Arrangement of the nodes may be anything but both BST should be Balanced.
Examples:
Input:
40
/ \
20 50
/ \ \
10 35 60
/ /
25 55
K = 35
Output:
First BST: 10 20 25
Second BST: 35 40 50 55 60
Explanation:
After splitting above BST
about given value K = 35
First Balanced Binary Search Tree is
20
/ \
10 25
Second Balanced Binary Search Tree is
50
/ \
35 55
\ \
40 60
OR
40
/ \
35 55
/ \
50 60
Input:
100
/ \
20 500
/ \
10 30
\
40
K = 50
Output:
First BST: 10 20 30 40
Second BST: 100 500
Explanation:
After splitting above BST
about given value K = 50
First Balanced Binary Search Tree is
20
/ \
10 30
\
40
Second Balanced Binary Search Tree is
100
\
500
Approach:
- First store the inorder traversal of given BST in an array
- Then, split this array about given value K
- Now construct first balanced BST by first splitting part and second BST by second splitting part, using the approach used in this article.
Below is the implementation of the above approach:
C++
// C++ program to split a BST into// two balanced BSTs based on a value K#include <iostream>using namespace std;// Structure of each node of BSTstruct node { int key; struct node *left, *right;};// A utility function to// create a new BST nodenode* newNode(int item){ node* temp = new node(); temp->key = item; temp->left = temp->right = NULL; return temp;}// A utility function to insert a new// node with given key in BSTstruct node* insert(struct node* node, int key){ // If the tree is empty, return a new node if (node == NULL) return newNode(key); // Otherwise, recur down the tree if (key < node->key) node->left = insert(node->left, key); else if (key > node->key) node->right = insert(node->right, key); // return the (unchanged) node pointer return node;}// Function to return the size// of the treeint sizeOfTree(node* root){ if (root == NULL) { return 0; } // Calculate left size recursively int left = sizeOfTree(root->left); // Calculate right size recursively int right = sizeOfTree(root->right); // Return total size recursively return (left + right + 1);}// Function to store inorder// traversal of BSTvoid storeInorder(node* root, int inOrder[], int& index){ // Base condition if (root == NULL) { return; } // Left recursive call storeInorder(root->left, inOrder, index); // Store elements in inorder array inOrder[index++] = root->key; // Right recursive call storeInorder(root->right, inOrder, index);}// Function to return the splitting// index of the arrayint getSplittingIndex(int inOrder[], int index, int k){ for (int i = 0; i < index; i++) { if (inOrder[i] >= k) { return i - 1; } } return index - 1;}// Function to create the Balanced// Binary search treenode* createBST(int inOrder[], int start, int end){ // Base Condition if (start > end) { return NULL; } // Calculate the mid of the array int mid = (start + end) / 2; node* t = newNode(inOrder[mid]); // Recursive call for left child t->left = createBST(inOrder, start, mid - 1); // Recursive call for right child t->right = createBST(inOrder, mid + 1, end); // Return newly created Balanced // Binary Search Tree return t;}// Function to traverse the tree// in inorder fashionvoid inorderTrav(node* root){ if (root == NULL) return; inorderTrav(root->left); cout << root->key << " "; inorderTrav(root->right);}// Function to split the BST// into two Balanced BSTvoid splitBST(node* root, int k){ // Print the original BST cout << "Original BST : "; if (root != NULL) { inorderTrav(root); } else { cout << "NULL"; } cout << endl; // Store the size of BST1 int numNode = sizeOfTree(root); // Take auxiliary array for storing // The inorder traversal of BST1 int inOrder[numNode + 1]; int index = 0; // Function call for storing // inorder traversal of BST1 storeInorder(root, inOrder, index); // Function call for getting // splitting index int splitIndex = getSplittingIndex(inOrder, index, k); node* root1 = NULL; node* root2 = NULL; // Creation of first Balanced // Binary Search Tree if (splitIndex != -1) root1 = createBST(inOrder, 0, splitIndex); // Creation of Second Balanced // Binary Search Tree if (splitIndex != (index - 1)) root2 = createBST(inOrder, splitIndex + 1, index - 1); // Print two Balanced BSTs cout << "First BST : "; if (root1 != NULL) { inorderTrav(root1); } else { cout << "NULL"; } cout << endl; cout << "Second BST : "; if (root2 != NULL) { inorderTrav(root2); } else { cout << "NULL"; }}// Driver codeint main(){ /* BST 5 / \ 3 7 / \ / \ 2 4 6 8 */ struct node* root = NULL; root = insert(root, 5); insert(root, 3); insert(root, 2); insert(root, 4); insert(root, 7); insert(root, 6); insert(root, 8); int k = 5; // Function to split BST splitBST(root, k); return 0;} |
Python3
# Python 3 program to split a# BST into two balanced BSTs# based on a value Kindex = 0# Structure of each node of BSTclass newNode: def __init__(self, item): # A utility function to # create a new BST node self.key = item self.left = None self.right = None# A utility function to insert# a new node with given key# in BSTdef insert(node, key): # If the tree is empty, # return a new node if (node == None): return newNode(key) # Otherwise, recur down # the tree if (key < node.key): node.left = insert(node.left, key) elif (key > node.key): node.right = insert(node.right, key) # return the (unchanged) # node pointer return node# Function to return the# size of the treedef sizeOfTree(root): if (root == None): return 0 # Calculate left size # recursively left = sizeOfTree(root.left) # Calculate right size # recursively right = sizeOfTree(root.right) # Return total size # recursively return (left + right + 1)# Function to store inorder# traversal of BSTdef storeInorder(root, inOrder): global index # Base condition if (root == None): return # Left recursive call storeInorder(root.left, inOrder) # Store elements in # inorder array inOrder[index] = root.key index += 1 # Right recursive call storeInorder(root.right, inOrder)# Function to return the# splitting index of the# arraydef getSplittingIndex(inOrder, index, k): for i in range(index): if (inOrder[i] >= k): return i - 1 return index - 1# Function to create the# Balanced Binary search# treedef createBST(inOrder, start, end): # Base Condition if (start > end): return None # Calculate the mid of # the array mid = (start + end) // 2 t = newNode(inOrder[mid]) # Recursive call for # left child t.left = createBST(inOrder, start, mid - 1) # Recursive call for # right child t.right = createBST(inOrder, mid + 1, end) # Return newly created # Balanced Binary Search # Tree return t# Function to traverse# the tree in inorder# fashiondef inorderTrav(root): if (root == None): return inorderTrav(root.left) print(root.key, end = " ") inorderTrav(root.right)# Function to split the BST# into two Balanced BSTdef splitBST(root, k): global index # Print the original BST print("Original BST : ") if (root != None): inorderTrav(root) print("\n", end = "") else: print("NULL") # Store the size of BST1 numNode = sizeOfTree(root) # Take auxiliary array for # storing The inorder traversal # of BST1 inOrder = [0 for i in range(numNode + 1)] index = 0 # Function call for storing # inorder traversal of BST1 storeInorder(root, inOrder) # Function call for getting # splitting index splitIndex = getSplittingIndex(inOrder, index, k) root1 = None root2 = None # Creation of first Balanced # Binary Search Tree if (splitIndex != -1): root1 = createBST(inOrder, 0, splitIndex) # Creation of Second Balanced # Binary Search Tree if (splitIndex != (index - 1)): root2 = createBST(inOrder, splitIndex + 1, index - 1) # Print two Balanced BSTs print("First BST : ") if (root1 != None): inorderTrav(root1) print("\n", end = "") else: print("NULL") print("Second BST : ") if (root2 != None): inorderTrav(root2) print("\n", end = "") else: print("NULL")# Driver codeif __name__ == '__main__': '''/* BST 5 / / 3 7 / / / / 2 4 6 8 */''' root = None root = insert(root, 5) insert(root, 3) insert(root, 2) insert(root, 4) insert(root, 7) insert(root, 6) insert(root, 8) k = 5 # Function to split BST splitBST(root, k)# This code is contributed by Chitranayal |
Output:
Original BST : 2 3 4 5 6 7 8 First BST : 2 3 4 Second BST : 5 6 7 8
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