文章标题

二叉树的相关知识点
1.四种遍历方法
2.更新树中的值
掌握重点：
1.对树要理解，以及其中的每个部分的意义
2.此学习代码是以二叉树为基础
3.理解前，中，后序遍历以及按层遍历，重点就是分清左右遍历与根节点遍历的先后顺序。
4.理解字符串（树的表示）中每个字符与树对应关系，这样才能用switch语句建立联系
5.遍历中使用了递归算法，要充分理解
6.知识点和链表有联系，注意两者间的联系
7.4和5代码红最重要的部分

include

include

define MAX 20

typedef char ElementType;

struct TreeNode
{
ElementType value;
struct TreeNode *left;
struct TreeNode *right;
};

void init(struct TreeNode** root);
void create(struct TreeNode** root, char *string);
void previsit(struct TreeNode* root);
void midvisit(struct TreeNode* root);
void tailvisit(struct TreeNode* root);
int treedepth(struct TreeNode* root);
void printtree(struct TreeNode* root);
void update(struct TreeNode* root, ElementType old_value, ElementType new_value);
void levelvisit(struct TreeNode* root);
void free(struct TreeNode* root);

int main()
{
struct TreeNode *root;
init(&root);
char *string = “A(B(D,E(G,H)),C(F( ,I)))”;
create(&root, string);
previsit(root);
printf(“\n”);
midvisit(root);
printf(“\n”);
tailvisit(root);
printf(“\n”);
printf(“depth = %d\n”, treedepth(root));
printtree(root);
printf(“\n”);
update(root, ‘A’, ‘Z’);
printtree(root);
printf(“\n”);
levelvisit(root);
printf(“\n”);
free(root);
printtree(root);
printf(“\n”);
return 0;
}

void init(struct TreeNode** root)
{
*root = NULL;
}
//A(B(D,E(G,H)),C(F( ,I)))
void create(struct TreeNode** root, char *string)
{
struct TreeNode *p;//用来存放新创建的节点
int i = 0;//用来遍历字符串的位置参数
int flag = 1;// 1:左树 2:右树
struct TreeNode* s[MAX];//模拟栈
int top = -1;//层数
while(*(string + i) != ‘\0’)
{
switch(*(string + i))
{
case ’ ‘:
break;
case ‘(‘:
if(top == MAX - 1)
{
printf(“tree is full\n”);
exit(1);
}
top++;
s[top] = p;
flag = 1;
//左子树的出现
break;
case ‘)’:
//右子树的结束
if (-1 == top)
{
printf(“error in string\n”);
exit;
}
top–;
break;
case ‘,’:
flag = 2;
//左子树切换到右子树
break;
default:
//遇到其他字符，代表新的节点出现
p = (struct TreeNode*)malloc(sizeof(struct TreeNode));
if (NULL == p)
{
exit(1);
}
//对value部分赋值
p->value = *(string + i);
//左右子树的处理
p->left = NULL;
p->right = NULL;
//root节点的处理
if (NULL == *root)
{
//暂时还未有root节点
//新创建的节点将成为root
*root = p;
}
else
{
//已经存在root
if (1 == flag)
{
//新建的节点是左树
s[top]->left = p;
}
else
{
//新建的节点是右树
s[top]->right = p;
}
}
break;
}
i++;
}
}

void previsit(struct TreeNode* root)
{
if (root != NULL)
{
printf(“%c\t”, root->value);
previsit(root->left);
previsit(root->right);
}
}

void midvisit(struct TreeNode* root)
{
if (root != NULL)
{
midvisit(root->left);
printf(“%c\t”, root->value);
midvisit(root->right);
}
}

void tailvisit(struct TreeNode* root)
{
if (root != NULL)
{
tailvisit(root->left);
tailvisit(root->right);
printf(“%c\t”, root->value);
}
}
void free(struct TreeNode* root)
{
if (root != NULL)
{
tailvisit(root->left);
tailvisit(root->right);
free(root);
}
}
int treedepth(struct TreeNode* root)
{
if (NULL == root)
{
return 0;
}
else
{
int depthleft = treedepth(root->left);
int depthright = treedepth(root->right);
return depthleft > depthright ? ++depthleft : ++depthright;
}
}

void printtree(struct TreeNode* root)
{
if (root != NULL)
{
printf(“%c”, root->value);
if (NULL != root->left || NULL != root->right)
{
printf(“(“);
if (NULL == root->left)
{
printf(” “);
}
else
{
printtree(root->left);
}
if (NULL == root->right)
{
printf(“, “);
}
else
{
printf(“,”);
printtree(root->right);
}
printf(“)”);
}
}
}

void update(struct TreeNode* root, ElementType old_value, ElementType new_value)
{
if (NULL != root)
{
update(root->left, old_value, new_value);
if (root->value == old_value)
{
root->value = new_value;
}
update(root->right, old_value, new_value);
}
}

void levelvisit(struct TreeNode* root)
{
struct TreeNode* p;
int front = 0;
int rear = 0;
struct TreeNode* array[MAX];

if (root != NULL){    //根元素入队    array[rear] = root;    rear = (rear + 1) % MAX;}while (front != rear){    p = array[front];    front = (front + 1) % MAX;    printf("%c\t", p->value);    if (NULL != p->left)    {        array[rear] = p->left;        rear = (rear + 1) % MAX;    }    if (NULL != p->right)    {        array[rear] = p->right;        rear = (rear + 1) % MAX;    }}

}

这里写代码片