前序遍历：根左右
中序遍历：左根右
后序遍历：左右根

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

//双链表节点结构
typedef struct treeNode {
	int value;
	struct treeNode* left;
	struct treeNode* right;
	treeNode(int x) : value(x), left(nullptr), right(nullptr) {}
} Node;

//前序遍历
void preOrder(Node* root, vector<int> &allval)
{
	if (!root)
	{
		return;
	}
	allval.push_back(root->value);  //遍历根节点
	preOrder(root->left, allval);   //遍历左节点
	preOrder(root->right, allval);  //遍历右节点
}

//中序遍历
void inOrder(Node* root, vector<int> &allval)
{
	if (!root)
	{
		return;
	}
	inOrder(root->left, allval);   //遍历左节点
	allval.push_back(root->value);  //遍历根节点
	inOrder(root->right, allval);  //遍历右节点
}

//后序遍历
void postOrder(Node* root, vector<int> &allval)
{
	if (!root)
	{
		return;
	}
	postOrder(root->left, allval);   //遍历左节点
	postOrder(root->right, allval);  //遍历右节点
	allval.push_back(root->value);  //遍历根节点
} 

int main()
{
	Node* root = new Node(1);
	root->left = new Node(2);
	root->right = new Node(3);
	root->left->left = new Node(4);
	root->left->right = new Node(5);
	//         1
	//      2     3
	//   4    5

	cout << "前序遍历结果：" << endl;  //12453
	vector<int> ves;
	preOrder(root, ves);
	for (int i = 0; i < ves.size(); i++)
	{
		cout << ves.at(i) << " ";
	}
	cout << endl;

	cout << "中序遍历结果：" << endl;  //42513
	vector<int> ves1;
	inOrder(root, ves1);
	for (int i = 0; i < ves1.size(); i++)
	{
		cout << ves1.at(i) << " ";
	}
	cout << endl;

	cout << "后序遍历结果：" << endl;  //45231
	vector<int> ves2;
	postOrder(root, ves2);
	for (int i = 0; i < ves2.size(); i++)
	{
		cout << ves2.at(i) << " ";
	}
	cout << endl;

	system("pause");
	return 0;
}