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 0
typedef 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; }