https://leetcode.com/problems/validate-binary-search-tree/
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1:
2
/ \
1 3
Input: [2,1,3] Output: true Example 2:
5
/ \
1 4
/ \
3 6
Input: [5,1,4,null,null,3,6] Output: false Explanation: The root node's value is 5 but its right child's value is 4.
https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
Given preorder and inorder traversal of a tree, construct the binary tree.
Note: You may assume that duplicates do not exist in the tree.
Can you do it both iteratively and recursively?
For example, given
preorder = [3,9,20,15,7]
inorder = [9,3,15,20,7] Return the following binary tree:
3
/ \
9 20
/ \
15 7