二叉排序树

#include 
#include 
#include 
#define KEY(n) (n ? n->key : -1)

typedef struct Node {
	int key;
	struct Node* lchild, * rchild;
} Node;

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

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

Node* predecessor(Node* root) {
	Node* tmp = root->lchild;
	while (tmp->rchild) tmp = tmp->rchild;
	return tmp;
}

Node* erase(Node* root, int key) {
	if (root == NULL) return root;
	if (key < root->key) 
		root->lchild = erase(root->lchild, key);
	else if (key > root->key) 
		root->rchild = erase(root->rchild, key);
	else {
		if (root->lchild == NULL && root->rchild == NULL) {
			free(root);
			return NULL;
		}
		else if (root->lchild == NULL || root->rchild == NULL) {
			Node* tmp = root->lchild ? root->lchild : root->rchild;
			free(root);
			return tmp;
		}
		else {
			//找前驱节点
			Node* tmp = predecessor(root);
			root->key = tmp->key;
			root->lchild = erase(root->lchild, tmp->key);
		}
	}
	return root;
}

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

void output(Node* root) {
	if (root == NULL) return;
	printf("(%2d : %2d, %2d)\n",
		KEY(root), 
		KEY(root->lchild), 
		KEY(root->rchild)
	);
	output(root->lchild);
	output(root->rchild);
	return;
}

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

int main() {
	srand(time(0));
#define MAX_OP 10
	Node* root = NULL;
	for (int i = 0; i < MAX_OP; i++) {
		int key = rand() % 100;
		printf("第 %2d 次操作：insert key %2d to BST\n", i + 1, key);
		root = insert(root, key);
	}
	output(root);
	printf("in order : ");
	in_order(root);
	int x;
	while (~scanf_s("%d", &x)) {
		printf("erase %d from BST\n", x);
		root = erase(root, x);
		in_order(root);
		printf("\n");
	}
	return 0;
}