树的几种遍历方式（递归/非递归）

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树的几种遍历方式，前序遍历，中序遍历，后序遍历，包括它的递归实现以及非递归实现

#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)//后序遍历{    if(root != NULL)    {        print(root->left);        print(root->right);        printf("%d\t",root->data);    }}void print1(pnode root)//前序遍历{    if(root != NULL)    {        printf("%d\t",root->data);        print(root->left);        print(root->right);    }}void print2(pnode root)//中序遍历{    if(root != NULL)    {        print(root->left);        printf("%d\t",root->data);        print(root->right);    }}void print3(pnode root) //层序遍历，队列存取{    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) //前序遍历非递归{    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) //中序遍历非递归实现{    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) //后序遍历非递归算法{    int top = -1;    pnode stack[50] = {NULL};    pnode prenode = NULL;    while(top != -1||root !=NULL)    {        while(root !=NULL)//一直找到最左节点        {            stack[++top] = root;            root = root->left;        }        root = stack[top];        if(root->right == NULL || root->right == prenode)//如果右节点被访问，或者右节点不存在        {            printf("%d\t",root->data);            prenode = root;            top--;            root = NULL;        }        else        {            root = root ->right;        }    }}
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