Validate Binary Search Tree

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Solution Guide: Validate Binary Search Tree

Approach

Track valid (min, max) range while recursing. Left subtree must stay below node value; right above.

Complexity Analysis

Time
O(n) where n is node count
Space
O(h) where h is tree height

Pattern

BST Constraint Validation

Why It Works

Each node narrows the allowed range for descendants; violating range means BST rule is broken.

Updated Feb 2026