#include<stdlib.h>
#include<stdio.h>
#include<assert.h>
//定义一个二叉树结点结构体
typedef int ElemTpye;
typedef struct TreeNode
{
	ElemTpye data;
	struct TreeNode* left;
	struct TreeNode* right;
}TreeNode;
//创建结点
TreeNode* createTreenode(ElemTpye data)
{
	TreeNode* newnode = (TreeNode*)malloc(sizeof(TreeNode));
	assert(newnode);
	newnode->data = data;
	newnode->left = NULL;
	newnode->right = NULL;
	return newnode;
}
//前序遍历  根左右
void preOrderTraversal(TreeNode* root)
{
	if (root == NULL)
	{
		return;
	}
	printf("%d ", root->data);
	preOrderTraversal(root->left);
	preOrderTraversal(root->right);
}
//中序遍历 左根右
void inOrderTraversal(TreeNode* root)
{
	if (root == NULL)
	{
		return;
	}

	inOrderTraversal(root->left);
	printf("%d ", root->data);
	inOrderTraversal(root->right);
}
//后序遍历 左右根
void postOrderTraversal(TreeNode* root)
{
	if (root == NULL)
	{
		return;
	}

	postOrderTraversal(root->left);
	postOrderTraversal(root->right);
	printf("%d ", root->data);
}
//层序遍历
void levelOrderTraversal(TreeNode* root)
{
	if (root == NULL)
	{
		return;
	}
	//设置一个队列（先进先出）
	TreeNode* queue[100];
	int front = 0, rear = 0;//头尾指针
	queue[rear++] = root;
	while (front < rear)
	{
		TreeNode* current = queue[front++];
		printf("%d ", current->data);

		if (current->left!= NULL)
		{
			queue[rear++] = current->left;
		}
		if (current->right != NULL)
		{
			queue[rear++] = current->right;
		}
	}
}
//释放二叉树空间
void freeTree(TreeNode* root)
{
	if (root == NULL)
	{
		return;
	}
	free(root->left);
	free(root->right);
	free(root);
}
int main()
{
	TreeNode* root = NULL;
	root = createTreenode(1);
	root->left = createTreenode(2);
	root->right = createTreenode(3);
	root->left->left = createTreenode(4);
	root->left->right = createTreenode(5);
	root->right->left = createTreenode(6);
	root->right->right = createTreenode(7);

	printf("前序遍历如下\n");
	preOrderTraversal(root);
	printf("\n");

	printf("中序遍历如下\n");
	inOrderTraversal(root);
	printf("\n");

	printf("后序遍历如下\n");
	postOrderTraversal(root);
	printf("\n");

	printf("层次遍历如下\n");
	levelOrderTraversal(root);
	printf("\n");

	freeTree(root);
	return 0;
}