[LeetCode]173. Binary Search Tree Iterator
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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.
Note: next()
and hasNext()
should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class BSTIterator { private Stack<TreeNode> stack; public BSTIterator(TreeNode root) { stack = new Stack<>(); TreeNode temp = root; while(temp!=null){ stack.push(temp); temp = temp.left; } } /** @return whether we have a next smallest number */ public boolean hasNext() { return !stack.isEmpty(); } /** @return the next smallest number */ public int next() { TreeNode temp = stack.pop(); if(temp.right!=null){ TreeNode right = temp.right; while(right!=null){ stack.push(right); right = right.left; } } return temp.val; }}/** * Your BSTIterator will be called like this: * BSTIterator i = new BSTIterator(root); * while (i.hasNext()) v[f()] = i.next(); */
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