Binary Search Tree Iterator

最新推荐文章于 2024-05-04 15:02:13 发布

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本文介绍了一种在二叉搜索树(BST)上实现迭代器的方法，该迭代器能够返回树中下一个最小的数值。文章详细展示了如何通过栈结构保存树节点，以确保平均时间复杂度为O(1)，空间复杂度为O(h)，其中h为树的高度。

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.

#include<iostream>
#include<vector>
#include<stack>
using namespace std;

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class BSTIterator {
public:
	stack<TreeNode*> StackMinNode;
	BSTIterator(TreeNode *root) {
		TreeNode* Curnode = root;
		while (Curnode)
		{
			StackMinNode.push(Curnode);
			Curnode = Curnode->left;
		}
	}

	/** @return whether we have a next smallest number */
	bool hasNext() {
		if (StackMinNode.empty())
			return false;
		else
			return true;
	}

	/** @return the next smallest number */
	int next() {
		TreeNode* tmp = StackMinNode.top();
		StackMinNode.pop();
		int val = tmp->val;
		tmp = tmp->right;
		while (tmp)
		{
			StackMinNode.push(tmp);
			tmp = tmp->left;
		}
		return val;
	}
};