树的前序，中序，后序遍历（递归）

描述

树的遍历即给出一个指向树的指针，访问树中的每一个节点。树的遍历有三种基本遍历方式，分别是前序（preorder）、中序（inorder）、后序（postorder）。

递归实现

原理

1. 前序（preorder）：先访问节点，然后访问该节点的左子树和右子树；
2. 中序（inorder） : 先访问该节点的左子树，然后访问该节点，再访问该节点的右子树；
3. 后序( postorder） : 先访问该节点的左子树和右子树，然后访问该节点。

代码实现

#include <stdlib.h>#include <stdio.h>#include <string.h>#define OK 1#define ERROR 0#define TRUE 1#define FALSE 0typedef char ElementType;typedef int Status;int index = 0;char str[] = "ABDH#K###E##CFI###G#J##";typedef struct TreeNode{    ElementType data;    struct TreeNode *Left;    struct TreeNode *Right;}TreeNode, *pTree;Status InitTree(pTree *T){    *T = NULL;    return OK;}Status Visit(pTree T){    if(T == NULL)        return ERROR;    printf("%c ",T->data);    return OK;}void DeleteTree(pTree *T){    if(*T)      {        if((*T)->Left)            DeleteTree(&(*T)->Left);        if((*T)->Right)            DeleteTree(&(*T)->Right);        free(*T);        *T = NULL;    }}void CreateTree(pTree *T){    ElementType ch;    ch = str[index++];    if(ch == '#')        *T = NULL;    else    {        *T = (pTree)malloc(sizeof(TreeNode));        if((*T) == NULL)            exit(0);        (*T)->data = ch;        CreateTree(&(*T)->Left);        CreateTree(&(*T)->Right);    }}int TreeDepth(pTree T){    int Ldepth, Rdepth;    if(T == NULL)        return -1;    if(T->Left)        Ldepth = TreeDepth(T->Left);    else         Ldepth = 0;    if(T->Right)        Rdepth = TreeDepth(T->Right);    else        Rdepth = 0;    return (Ldepth > Rdepth)? Ldepth + 1 : Rdepth + 1;}int TreeNodeCount(pTree T){    if( T == NULL)        return 0;    return TreeNodeCount(T->Left) + TreeNodeCount(T->Right) + 1;}int TreeIsEmpty(pTree T){    if(T)        return FALSE;    else         return TRUE;}void PreorderTraverse(pTree T, Status (*Visit)(pTree)){    if(T == NULL)        return;    (*Visit)(T);    //printf("%c ",T->data);    PreorderTraverse(T->Left,Visit);    PreorderTraverse(T->Right,Visit);}void InorderTraverse(pTree T, Status (*Vistit)(pTree)){    if(T == NULL)        return;    InorderTraverse(T->Left,Visit);    (*Visit)(T);    InorderTraverse(T->Right,Visit);}void PostorderTraverse(pTree T, Status (*Visit)(pTree)){    if(T == NULL)        return;    PostorderTraverse(T->Left,Visit);    PostorderTraverse(T->Right,Visit);    (*Visit)(T);}int main(){    pTree Tree;    InitTree(&Tree);    CreateTree(&Tree);    printf("Tree's Depth is %d\n",TreeDepth(Tree));    printf("Tree's Node number is %d\n",TreeNodeCount(Tree));    if(TreeIsEmpty(Tree))    {        printf("Tree is Empty\n");    }    printf("PreorderTraverse is :");    PreorderTraverse(Tree,Visit);    printf("\n");    printf("InorderTraverse is :");    InorderTraverse(Tree,Visit);    printf("\n");    printf("PostorderTraverse is :");    PostorderTraverse(Tree,Visit);    printf("\n");    DeleteTree(&Tree);    if(TreeIsEmpty(Tree))    {        printf("Tree is Delte and Empty\n");    }    return 0;}