LeetCode Binary Tree Zigzag Level Order Traversal

最新推荐文章于 2021-02-05 11:10:39 发布

原创最新推荐文章于 2021-02-05 11:10:39 发布 · 491 阅读

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本文介绍了一种二叉树的锯齿形层序遍历算法实现，通过记录节点所在的层级来判断是否需要反转当前层的节点值顺序。文章提供了完整的C++代码示例，并展示了如何构建一个简单的二叉树进行测试。

比上一题多两行代码，就是在装入结果集时判断当前层数是奇是偶。这题要是更改遍历的方式，按照左子树右子树，右子树左子树的方式遍历恐怕要很难处理。

// LeetCode_BinaryTreeLevelOrderTraversal.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;

struct TreeNode {
	     int val;
	     TreeNode *left;
	     TreeNode *right;
	     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
	 };
struct QueNode{
	int num;
	TreeNode *pTreeNode;
	QueNode():num(0),pTreeNode(NULL){}
};

vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
	vector<vector<int> >ret;
	vector<int> oneresult,tempResult;
	if(root==NULL)
		return ret;
	queue<QueNode> que;
	QueNode qn;
	qn.num = 0;
	qn.pTreeNode = root;
	que.push(qn);
	QueNode tempNode,tempLeftNode,tempRightNode;
	int lastnum = 0;
	while(!que.empty())
	{
		tempNode = que.front();
		que.pop();
		if (lastnum!=tempNode.num)
		{
			if(tempNode.num%2==0)
				reverse(oneresult.begin(),oneresult.end());
			ret.push_back(oneresult);
			oneresult.clear();
			oneresult.push_back(tempNode.pTreeNode->val);
			lastnum = tempNode.num;
		}
		else
			oneresult.push_back(tempNode.pTreeNode->val);
		if (tempNode.pTreeNode->left)
		{
			tempLeftNode.num = tempNode.num+1;
			tempLeftNode.pTreeNode = tempNode.pTreeNode->left;
			que.push(tempLeftNode);
		}
		if (tempNode.pTreeNode->right)
		{
			tempRightNode.num = tempNode.num+1;
			tempRightNode.pTreeNode = tempNode.pTreeNode->right;
			que.push(tempRightNode);
		}	
	}
	if(lastnum%2!=0)
		reverse(oneresult.begin(),oneresult.end());
	ret.push_back(oneresult);
	oneresult.clear();
	return ret;
}

int _tmain(int argc, _TCHAR* argv[])
{
	TreeNode *pa = new TreeNode(1);
	TreeNode *pb = new TreeNode(2);
	TreeNode *pc = new TreeNode(3);
	TreeNode *pd = new TreeNode(4);//TreeNode *pd = NULL;//
	TreeNode *pe = new TreeNode(5);
	TreeNode *pf = NULL;//TreeNode *pf = new TreeNode(3);
	TreeNode *pg = new TreeNode(6);
	pa->left = pb;
	pa->right = pc;
	pb->left = pd;
	pb->right = pe;
	pc->left = pf;
	pc->right = pg;
	vector<vector<int> >ret;
	//ret = levelOrder(pa);
	vector<vector<int> >rret;
	rret = zigzagLevelOrder(pa);
	system("pause");
	return 0;
}