Problem: Validate Binary Search Tree
Understand how to validate a binary search tree by ensuring each node adheres to strict key ordering rules. Learn a recursive method in C# that checks node values within boundary ranges and returns true if the tree meets BST properties. This lesson explains constraints, provides a clear solution approach, and analyzes time and space complexity.
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Statement
Given the root of a binary tree, determine whether it is a valid binary search tree (BST).
A valid BST satisfies the following properties:
The left subtree of every node contains only nodes with keys strictly less than that node’s key.
The right subtree of every node contains only nodes with keys strictly greater than that node’s key.
Both the left and right subtrees must themselves be valid binary search trees.
Return true if the given binary tree is a valid BST, and false otherwise.
Constraints:
The number of nodes in the tree is in the range
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