樹的幾種遍歷方式，前序遍歷，中序遍歷，後序遍歷，包括它的遞迴實現以及非遞迴實現

#include<stdio.h>
#include<stdlib.h>
typedef struct tree
{

    int data;
    struct tree *left;
    struct tree *right;
    int flag ;

}*pnode,node;

pnode createbinary(int a[],int n,pnode p);
pnode insertNode(int data,pnode root);
void print(pnode root);
void
 
 print1(pnode root);
void print2(pnode root);
void print3(pnode root);
void print4(pnode root);
void print5(pnode root);
void print6(pnode root);
void main()
{

    int a[9] = {6,3,8,5,2,9,4,7,11};
    pnode root = NULL;
    root = createbinary(a,9,root);
    print6(root);
    free(root);

}
pnode createbinary(int
 
 a[],int n,pnode root)
{
    for(int i=0; i<n; i++)
    {
        root = insertNode(a[i],root);
    }
    return root;
}
pnode insertNode(int value,pnode root)
{
    pnode currentnode;
    pnode parentnode;
    pnode newnode = (pnode)malloc(sizeof(node));
    newnode->data = value;
    newnode->left = NULL
 
;
    newnode->right = NULL;

    if(root == NULL)
    {
        root = newnode;
    }
    else
    {
        currentnode = root;
        while(currentnode != NULL)
        {
            parentnode = currentnode;
            if(currentnode->data > value)
                currentnode = currentnode->left;
            else
                currentnode = currentnode->right;
        }
        if(parentnode->data > value)
        {
            parentnode->left = newnode;
        }
        else
        {
            parentnode->right = newnode;
        }
    }
    return root;
}
void print(pnode root)//後序遍歷
{
    if(root != NULL)
    {
        print(root->left);
        print(root->right);
        printf("%d\t",root->data);

    }

}
void print1(pnode root)//前序遍歷
{

    if(root != NULL)
    {
        printf("%d\t",root->data);
        print(root->left);
        print(root->right);

    }

}
void print2(pnode root)//中序遍歷
{

    if(root != NULL)
    {
        print(root->left);
        printf("%d\t",root->data);
        print(root->right);

    }

}
void print3(pnode root) //層序遍歷，佇列存取
{

    pnode q = NULL;
    pnode Q[50]= {NULL};
    int front = -1,rear = -1;
    if(root == NULL)
    {
        return ;
    }
    Q[++rear] = root;
    while(front != rear)
    {

        q = Q[++front];
        printf("%d\t",q->data);
        if(q->left != NULL)
            Q[++rear] = q->left;
        if(q->right != NULL)
            Q[++rear] = q->right;

    }
}
void print4(pnode root) //前序遍歷非遞迴
{

    int top = -1;
    pnode stack[50] = {NULL};
    while(top != -1||root != NULL)
    {

        while(root != NULL)
        {

            printf("%d\t",root->data);
            stack[++top] = root;
            root = root->left;

        }
        if(top != -1)
        {
            root = stack[top--];
            root = root->right;
        }
    }
}
void print5(pnode root) //中序遍歷非遞迴實現
{

    int top = -1;
    pnode stack[50] = {NULL};
    while(top != -1||root != NULL)
    {

        while(root != NULL)
        {

            stack[++top] = root;
            root = root->left;

        }
        if(top != -1)
        {
            root = stack[top--];
            printf("%d\t",root->data);
            root = root->right;
        }
    }
}
void print6(pnode root) //後序遍歷非遞迴演算法
{

    int top = -1;
    pnode stack[50] = {NULL};
    pnode prenode = NULL;
    while(top != -1||root !=NULL)
    {

        while(root !=NULL)//一直找到最左節點
        {

            stack[++top] = root;
            root = root->left;
        }
        root = stack[top];
        if(root->right == NULL || root->right == prenode)//如果右節點被訪問，或者右節點不存在
        {
            printf("%d\t",root->data);
            prenode = root;
            top--;
            root = NULL;
        }
        else
        {
            root = root ->right;
        }

    }

}