1 #include <stdio.h>
2 #include <stdlib.h>
3
4 typedef enum
5 {
6 Link,
7 Tread
8 }PointerTag;
9
10 typedef char TElemType;
11
12 typedef struct TreeNode
13 {
14 TElemType data; //数据单元
15
16 struct TreeNode *pLChild, *pRChild; //左右孩子指针
17 PointerTag LTag, RTag; //左右标志 ==0：孩子指针；==1：前后驱
18 }TreeNode, Tree;
19
20 TreeNode *gPre = NULL;
21
22 /* 先序创建二叉树 */
23 void CreateTree(Tree **_t)
24 {
25 TElemType ch = -1;
26
27 scanf("%c", &ch);
28
29 if(ch == '#')
30 *_t = NULL;
31 else
32 {
33 *_t = (Tree*)malloc(sizeof(TreeNode));
34 if(*_t == NULL)
35 return;
36 (*_t)->data = ch;
37 (*_t)->LTag = Link;
38 (*_t)->RTag = Link;
39 CreateTree(&((*_t)->pLChild));
40 CreateTree(&((*_t)->pRChild));
41 }
42 }
43
44 /* 遍历二叉树 */
45 int InOrderThraverse_Thr(Tree *_t)
46 {
47 Tree *p =NULL;
48
49 p = _t->pLChild;
50 while(p != _t)
51 {
52 while(p->LTag == Link)
53 p = p->pLChild;
54
55 printf("%c ", p->data); //对节点的操作
56
57 while((p->RTag == Tread) && (p->pRChild != _t))
58 {
59 p = p->pRChild;
60
61 printf("%c ", p->data);
62 }
63 p = p->pRChild;
64 }
65
66 return 0;
67 }
68
69 void InOrderThreading(Tree *_p)
70 {
71 if(_p)
72 {
73 InOrderThreading(_p->pLChild); //左树线索初始化
74 if(!_p->pLChild) //前驱线索
75 {
76 _p->LTag = Tread;
77 _p->pLChild = gPre;
78 }
79 if(!gPre->pRChild) //后继线索
80 {
81 gPre->RTag = Tread;
82 gPre->pRChild = _p;
83 }
84 gPre = _p;
85
86 InOrderThreading(_p->pRChild); //右子树线索初始化
87 }
88 }
89
90 /* 线索化二叉树 */
91 int InOrderThread_Head(Tree **_h, Tree *_t)
92 {
93 (*_h) = (TreeNode *)malloc(sizeof(TreeNode));
94 if(*_h == NULL)
95 return -1;
96
97 (*_h)->pRChild = *_h;
98 (*_h)->RTag = Link;
99
100 if(!_t)
101 {
102 (*_h)->pLChild = *_h;
103 (*_h)->LTag = Link;
104 }
105 else
106 {
107 gPre = *_h;
108 (*_h)->LTag = Link;
109 (*_h)->pLChild = _t;
110 InOrderThreading(_t);
111 gPre->pRChild = *_h;
112 gPre->RTag = Tread;
113 (*_h)->pRChild = gPre;
114 }
115
116 return 0;
117 }
118
119 int main(void)
120 {
121 Tree *t=NULL, *temp=NULL;
122
123 printf("请输入前序二叉树的内容：\n");
124 CreateTree(&t);
125 InOrderThread_Head(&temp, t); //加入头结点，并线索化
126 printf("输出中序二叉树的内容:\n");
127 InOrderThraverse_Thr(temp);
128
129 printf("\n");
130 return 0;
131 }
mrrs@ubuntu:~/Desktop/DSC$ ./test
请输入前序二叉树的内容：
ABDG##H###CE#I##F##
输出中序二叉树的内容:
G D H B A E I C F
