1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <stdbool.h>
  4 
  5 typedef int DATA;
  6 typedef struct _SNode_
  7 {
  8     DATA data;
  9     struct _SNode_ *p_Right, *p_Left;
 10 }SNode;
 11 
 12 SNode *CreateTree(const DATA d)
 13 {
 14     SNode *m_root = (SNode *)malloc(sizeof(SNode));
 15     m_root->data = d;
 16     m_root->p_Left = m_root->p_Right = NULL;
 17     return m_root;
 18 }
 19 
 20 void InsertRight(SNode *p, const DATA d)
 21 {
 22     SNode *pNew = CreateTree(d);
 23     p->p_Right = pNew;
 24 }
 25 
 26 void InsertLeft(SNode *p, const DATA d)
 27 {
 28     SNode *pNew = CreateTree(d);
 29     p->p_Left = pNew;
 30 }
 31 
 32 void PreOrder(SNode *p)
 33 {
 34     printf("%d ", p->data);
 35     if (p->p_Left)
 36         PreOrder(p->p_Left);
 37     if (p->p_Right)
 38         PreOrder(p->p_Right);
 39 }
 40 
 41 void InOrder(SNode *p)
 42 {
 43     if (p->p_Left)
 44         InOrder(p->p_Left);
 45     printf("%d ", p->data);
 46     if (p->p_Right)
 47         InOrder(p->p_Right);
 48 }
 49 
 50 void PostOrder(SNode *p)
 51 {
 52     if (p->p_Left)
 53         PostOrder(p->p_Left);
 54     if (p->p_Right)
 55         PostOrder(p->p_Right);
 56     printf("%d ", p->data);
 57 }
 58 
 59 bool LookUp(SNode *p, const DATA d)
 60 {
 61     while (p)
 62     {
 63         if (p->data == d)
 64             return true;
 65         else if (p->data > d)
 66             p = p->p_Left;
 67         else
 68             p = p->p_Right;
 69     }
 70     return false;
 71 }
 72 
 73 // 方式二：使用二级指针
 74 void SetAt(SNode *p, const DATA d) // 创建搜索二叉树
 75 {
 76     if (p == NULL)
 77     {
 78         p = CreateTree(d);
 79         return;
 80     }
 81     SNode **ppRoot = &p;
 82     while (*ppRoot)
 83     {
 84         if ((*ppRoot)->data < d)
 85             ppRoot = &(*ppRoot)->p_Right;
 86         else if ((*ppRoot)->data > d)
 87             ppRoot = &(*ppRoot)->p_Left;
 88     }
 89     SNode *pNew = CreateTree(d);
 90     *ppRoot = pNew;
 91 }
 92 
 93 int main()
 94 {
 95     SNode *pRoot = CreateTree(30);
 96     SetAt(pRoot, 75);
 97     SetAt(pRoot, 20);
 98     SetAt(pRoot, 40);
 99     SetAt(pRoot, 10);
100     SetAt(pRoot, 60);
101     SetAt(pRoot, 50);
102 
103     if (LookUp(pRoot, 52))
104         printf("找到了！\n");
105     else
106         printf("没有找到！\n");
107 
108     InOrder(pRoot);
109 
110     return 0;
111 }