树的遍历非递归实现

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <algorithm>
#include <map>
#include <vector>
#include <set>
#include <queue>
#include <stack>
#include <math.h>


using namespace std;

struct Node
{
    int val;
    Node* left;
    Node* right;
    Node(int value)
    {
        this->val = value;
        this->left=NULL;
        this->right=NULL;
    }
};

void preOrder(Node* root)
{
    if(root==NULL)
        return;
    cout<<root->val;
    preOrder(root->left);
    preOrder(root->right);
}

void inOrder(Node* root)
{
    if(root==NULL)
        return;

    inOrder(root->left);
    cout<<root->val;
    inOrder(root->right);
}

void postOrder(Node* root)
{
    if(root==NULL)
        return;

    postOrder(root->left);

    postOrder(root->right);
    cout<<root->val;

}
void buildTree(Node* &tree)
{
    tree = new Node(4);
    tree->left = new Node(3);
    tree->left->left = new Node(5);
    //tree->left->left->right = new Node(10);
    //tree->left->left->right->left = new Node(11);
    tree->left->right = new Node(6);
    tree->right = new Node(7);
    tree->right->left = new Node(8);
    tree->right->right = new Node(9);
}

int main()
{

    Node* tree;
    buildTree(tree);
    preOrder(tree);
    cout<<endl;
    stack<Node*> s;
    s.push(tree);

    while(!s.empty())
    {
        Node* temp = s.top();
        s.pop();

        cout<<temp->val;
        if(temp->right!=NULL)
            s.push(temp->right);
        if(temp->left!=NULL)
            s.push(temp->left);
    }

    cout<<endl;

    Node* tree2=tree;
    cout << tree->val;
    s.push(tree);

    while(!s.empty()) {

        Node *temp = s.top();

        if (temp->left != NULL) {
            cout << temp->left->val;
            s.push(temp->left);
            temp->left=NULL;
            continue;
        }

        s.pop();
        if (temp->right != NULL) {
            cout << temp->right->val;
            s.push(temp->right);
            temp->right=NULL;
            continue;
        }


    }
    cout<<endl;

    buildTree(tree);
    Node* temp = tree;
    while(!s.empty()||temp!=NULL)
    {
        if(temp!=NULL)
        {
            cout<<temp->val;
            s.push(temp);
            temp=temp->left;
        }
        else
        {
            temp = s.top();
            s.pop();
            temp = temp->right;
        }
    }
    cout<<endl;

    inOrder(tree);

    cout<<endl;

    s.push(tree);

    while(!s.empty())
    {
        Node* temp = s.top();
        if(temp->left!=NULL)
        {
            s.push(temp->left);
            temp->left=NULL;
            continue;
        }
        cout<<temp->val;
        s.pop();
        if(temp->right!=NULL)
        {
            s.push(temp->right);
            temp->right=NULL;
            continue;
        }
    }

    cout<<endl;
    buildTree(tree);
    temp = tree;
    while(!s.empty()||temp!=NULL)
    {
        if(temp!=NULL)
        {
            s.push(temp);
            temp=temp->left;
        } else{
            temp = s.top();
            cout<<temp->val;
            s.pop();
            temp = temp->right;
        }
    }
    cout<<endl;
    buildTree(tree);

    postOrder(tree);
    cout<<endl;
    s.push(tree);

    while(!s.empty())
    {
        Node* temp = s.top();
        if(temp->left!=NULL)
        {
            s.push(temp->left);
            temp->left=NULL;
            continue;
        }
        if(temp->right!=NULL)
        {
            s.push(temp->right);
            temp->right=NULL;
            continue;
        }
        s.pop();
        cout<<temp->val;
    }

    cout<<endl;
    buildTree(tree);

    s.push(tree);

    vector<int> ans;

    while(!s.empty())
    {
        Node* temp = s.top();
        s.pop();

        ans.push_back(temp->val);
        if(temp->left!=NULL)
            s.push(temp->left);
        if(temp->right!=NULL)
            s.push(temp->right);
    }

    for(int i=ans.size()-1;i>=0;i--)
        cout<<ans[i];

    return 0;
}