接口

typedef char BTDataType;

typedef struct BinaryTreeNode {
	BTDataType _data;
	struct BinaryTreeNode* _left;
	struct BinaryTreeNode* _right;
}BTNode;

// 通过前序遍历的数组"ABD##E#H##CF##G##"构建二叉树 
BTNode* BinaryTreeCreate(BTDataType* a, int* pi); 
void BinaryTreeDestory(BTNode** root);

int BinaryTreeSize(BTNode* root);
int BinaryTreeLeafSize(BTNode* root);
int BinaryTreeLevelKSize(BTNode* root, int k);
BTNode* BinaryTreeFind(BTNode* root, BTDataType x);
// 遍历
void BinaryTreePrevOrder(BTNode* root); 
void BinaryTreeInOrder(BTNode* root); 
void BinaryTreePostOrder(BTNode* root);

实现

#include "BinaryTree.h"

// 通过前序遍历的数组"ABD##E#H##CF##G##"构建二叉树 
BTNode* BinaryTreeCreate(BTDataType* a, int* pi){
	if (a[*pi] != '#'){
		//创建根节点
		BTNode* root = (BTNode*)malloc(sizeof(BTNode));
		root->_data = a[*pi];
		//创建左节点
		(*pi)++;
		root->_left = BinaryTreeCreate(a, pi);
		//创建右节点
		(*pi)++;
		root->_right = BinaryTreeCreate(a, pi);
		return root;
	}
	else
		return NULL;
}
//想要把指针置空, 需要传二级指针, (传的是指针的copy)
void BinaryTreeDestory(BTNode** root){
	if (*root){
		BinaryTreeDestory(&(*root)->_left);
		BinaryTreeDestory(&(*root)->_right);
		free(*root);
		*root = NULL;
	}
}

//有效节点的个数
int BinaryTreeSize(BTNode* root){
	if (root != NULL){
		return BinaryTreeSize(root->_left) +
			BinaryTreeSize(root->_right) + 1;
	}
	else
		return 0;
}
//叶子的个数
int BinaryTreeLeafSize(BTNode* root){
	if (root == NULL){
		return 0;
	}
	if (root->_left == NULL && root->_right == NULL){
		return 1;
	}
	return BinaryTreeLeafSize(root->_left) + BinaryTreeLeafSize(root->_right);
}

//第 k 层的节点个数
int BinaryTreeLevelKSize(BTNode* root, int k){
	if (root == NULL){
		return 0;
	}
	if (k == 1){
		return 1;
	}
	return BinaryTreeLevelKSize(root->_left, k - 1) +
		BinaryTreeLevelKSize(root->_right, k - 1);
}

//找到 x
BTNode* BinaryTreeFind(BTNode* root, BTDataType x){
	BTNode* ret;
	if (root == NULL){
		return NULL;
	}
	//根节点
	if (root->_data == x){
		return root;
	}
	//找左子树
	ret = BinaryTreeFind(root->_left, x);
	if (ret){
		return ret;
	}
	//左子树找不到, 找右子树
	ret = BinaryTreeLeafSize(root->_right, x);
	if (ret){
		return ret;
	}
	//没找到
	return NULL;
}

//前序 遍历
void BinaryTreePrevOrder(BTNode* root){
	//先打印根节点
	//访问根的左子树
	//访问根的右子树
	if (root){
		printf("%c ", root->_data);
		BinaryTreePrevOrder(root->_left);
		BinaryTreePrevOrder(root->_right);
	}
}
//中序遍历
void BinaryTreeInOrder(BTNode* root){
	if (root){
		BinaryTreeInOrder(root->_left);
		printf("%c ", root->_data);
		BinaryTreeInOrder(root->_right);
	}
}
//后序遍历
void BinaryTreePostOrder(BTNode* root){
	if (root){
		BinaryTreePostOrder(root->_left);
		BinaryTreePostOrder(root->_right);
		printf("%c ", root->_data);
	}
}