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Leetcode 173. Binary Search Tree Iterator
Implement an iterator over a BST that returns elements in in-order (ascending) via next() and hasNext(), starting before the smallest element so the first next() yields the minimum. Aim for next()/hasNext() to handle up to 1e5 calls with amortized O(1) time and O(h) extra space (h = tree height).
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Early October, 2025
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