Given a binary tree, find the largest subtree which is a Binary Search Tree (BST), where largest means subtree with largest number of nodes in it.
Note: A subtree must include all of its descendants. Here's an example:
10
/ \
5 15
/ \ \
1 8 7
The Largest BST Subtree in this case is the highlighted one. The return value is the subtree's size, which is 3.
Hint:
You can recursively use algorithm similar to 98. Validate Binary Search Tree at each node of the tree, which will result in O(nlogn) time complexity.
Follow up:
Can you figure out ways to solve it with O(n) time complexity?