Given a binary search tree, the task is to flatten it to a sorted list. Precisely, the value of each node must be lesser than the values of all the nodes at its right, and its left node must be NULL after flattening. We must do it in O(H) extra space where ‘H’ is the height of BST.
Input: 5 / \ 3 7 / \ / \ 2 4 6 8 Output: 2 3 4 5 6 7 8 Input: 1 \ 2 \ 3 \ 4 \ 5 Output: 1 2 3 4 5
Approach: A simple approach will be to recreate the BST from its in-order traversal. This will take O(N) extra space were N is the number of node in BST.
To improve upon that, we will simulate in order traversal of a binary tree as follows:
- Create a dummy node.
- Create a variable called ‘prev’ and make it point to the dummy node.
- Perform in-order traversal and at each step.
- Set prev -> right = curr
- Set prev -> left = NULL
- Set prev = curr
This will improve the space complexity to O(H) in worst case as in-order traversal takes O(H) extra space.
Below is the implementation of the above approach:
2 3 4 5 6 7 8
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- Flatten BST to sorted list | Decreasing order
- Flatten Binary Tree in order of Level Order Traversal
- Flatten binary tree in order of post-order traversal
- Find k-th smallest element in BST (Order Statistics in BST)
- Flatten Binary Tree in order of Zig Zag traversal
- Sorted order printing of a given array that represents a BST
- Build Binary Tree from BST such that it's level order traversal prints sorted data
- Flatten a binary tree into linked list
- Flatten a binary tree into linked list | Set-2
- Flatten a binary tree into linked list | Set-3
- Sorted Linked List to Balanced BST
- K'th Largest Element in BST when modification to BST is not allowed
- Convert a normal BST to Balanced BST
- Two nodes of a BST are swapped, correct the BST | Set-2
- Two nodes of a BST are swapped, correct the BST
- Sorted Array to Balanced BST
- Construct BST from its given level order traversal
- Construct BST from its given level order traversal | Set-2
- Sort only non-prime numbers of an array in increasing order
- Print array elements in alternatively increasing and decreasing order
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