二叉树的遍历和线索化（线索化用中序线索化举例）

#include 
#include 
#include 

typedef struct Node {
	int ltag, rtag;//1代表线索0代表边
	int key;
	struct Node* lchild, * rchild;
} Node;

Node* getNewNode(int key) {
	Node* p = (Node*)malloc(sizeof(Node));
	p->ltag = p->rtag = 0;
	p->key = key;
	p->lchild = p->rchild = NULL;
	return p;
} 

Node* insert(Node* root, int key) {
	if (root == NULL) return getNewNode(key);
	if (rand() % 2) root->lchild = insert(root->lchild, key);
	else root->rchild = insert(root->rchild, key);
	return root;
}

void clear(Node* root) {
	if (root == NULL) return;
	if (root->ltag == 0) clear(root->lchild);
	if (root->rtag == 0) clear(root->rchild);
	free(root);
	return;
}

void pre_order(Node* root) {
	if (root == NULL) return;
	printf("%d ", root->key);
	if (root->ltag == 0) pre_order(root->lchild);
	if (root->rtag == 0) pre_order(root->rchild);
	return;
}

void in_order(Node* root) {
	if (root == NULL) return;
	if (root->ltag == 0) in_order(root->lchild);
	printf("%d ", root->key);
	if (root->rtag == 0) in_order(root->rchild);
	return;
}

void post_order(Node* root) {
	if (root == NULL) return;
	if (root->ltag == 0) post_order(root->lchild); 
	if (root->rtag == 0) post_order(root->rchild);
	printf("%d ", root->key);
	return;
}

Node* pre_node = NULL, *inorder_root = NULL;
void __inorder_thread(Node* root) {
	if (root == NULL) return;
	if (root->ltag == 0) __inorder_thread(root->lchild);
	if (inorder_root == NULL) inorder_root = root;
	if (root->lchild == NULL) {
		root->lchild = pre_node;
		root->ltag = 1;
	}
	if (pre_node != NULL && pre_node->rchild == NULL) {
		pre_node->rchild = root;
		pre_node->rtag = 1;
	}
	pre_node = root;
	if (root->rtag == 0) __inorder_thread(root->rchild);
	return;
}

void inorder_thread(Node* root) {
	__inorder_thread(root);
	pre_node->rchild = NULL;
	pre_node->rtag = 1;
	return;
}

Node* getNext(Node* root) {
	if (root->rtag == 1) return root->rchild;
	root = root->rchild;
	while (root->ltag == 0 && root->lchild) root = root->lchild; 
	return root;
}

int main() {
	srand(time(0));
	Node* root = NULL;
#define MAX_SIZE 10
	for (int i = 0; i < MAX_SIZE; i++) {
		root = insert(root, rand() % 100);
	}
	inorder_thread(root);
	pre_order(root);  printf("\n");
	in_order(root);   printf("\n");
	post_order(root); printf("\n");

	Node* node = inorder_root;
	while (node != NULL) {
		printf("%d ", node->key);
		node = getNext(node);
	}
	printf("\n");
	clear(root);
	return 0;
}