README_EN.md

173. Binary Search Tree Iterator

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Description

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.

Calling next() will return the next smallest number in the BST.

 

Example:

BSTIterator iterator = new BSTIterator(root);

iterator.next();    // return 3

iterator.next();    // return 7

iterator.hasNext(); // return true

iterator.next();    // return 9

iterator.hasNext(); // return true

iterator.next();    // return 15

iterator.hasNext(); // return true

iterator.next();    // return 20

iterator.hasNext(); // return false

 

Note:

• next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
• You may assume that next() call will always be valid, that is, there will be at least a next smallest number in the BST when next() is called.

Solutions

Python3

Java

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