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"Don't memorize solutions. Memorize the **Recursive Shapes**. Once you understand how state flows up and down a tree, you can solve 80% of LeetCode Tree problems."
Categorized recursive strategies for FAANG interviews.
"Solve for subtrees, then combine answers at the parent."
"Pass boundary information (min/max) down to children."
"Process layer-by-layer using a breadth-first queue."
"Walk two trees at the same time to check symmetry or identity."
"Switch problems to analyze recursive state flow."
"Determine if a binary tree is a valid Binary Search Tree."
"DFS with Min/Max range constraints."
**Pro Tip**: In Validate BST, the base case is the most important part. Always define when the recursion must stop to avoid stack overflow.
1function isValidBST(root, min = -Infinity, max = Infinity) {2 if (!root) return true;3 if (root.val <= min || root.val >= max) return false;4 5 return isValidBST(root.left, min, root.val) && 6 isValidBST(root.right, root.val, max);7}"You've moved from linear pointers to branching hierarchies. You're now ready for Module 6: Heaps & Priority Queues."