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 {Stack<TreeNode> stack = new Stack<TreeNode>(); public BSTIterator(TreeNode root) { pushAll(root); } /** @return whether we have a next smallest number */ public boolean hasNext() { return !stack.isEmpty(); } /** @return the next smallest number */ public int next() { if(stack.isEmpty()) return Integer.MAX_VALUE; TreeNode node = stack.pop(); pushAll(node.right); return node.val; } public void pushAll(TreeNode root){ while(root != null){ stack.push(root); root = root.left; } }}/** * Your BSTIterator will be called like this: * BSTIterator i = new BSTIterator(root); * while (i.hasNext()) v[f()] = i.next(); */新闻热点
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