一步一步复习数据机构和算法基础-二叉树创建（前序建立二叉树）

最基础的二叉树：

#include <stdio.h>
#include <stdlib.h>

typedef int elemtype;		//整形为树的数据类型
typedef struct node
{
	elemtype data;
	struct node *lchild,*rchild;
}btree,*ptree;

void (*visit)(elemtype e);

//树的创建
ptree CreatTree()
{
	ptree root;
	elemtype data;
	scanf("%d",&data);

	if(data == 0)root = NULL;		//0 代表空子树
	else
	{
		root = (ptree)malloc(sizeof(btree));
		if(!root)exit(1);

		root->data = data;
		root->lchild = CreatTree();
		root->rchild = CreatTree();
	}
	return root;
}

void PrintResult(elemtype e)
{
	printf("%d ",e);
}

//前序遍历二叉树
void PreOrderTree(ptree root,void (*visit)(elemtype ))
{
	if(root)
	{
		(visit)(root->data);
		PreOrderTree(root->lchild,visit);
		PreOrderTree(root->rchild,visit);
	}
}

//中序遍历二叉树
void InOrderTree(ptree root,void (*visit)(elemtype ))
{
	if(root)
	{
		PreOrderTree(root->lchild,visit);
		(visit)(root->data);
		PreOrderTree(root->rchild,visit);
	}
}

//后序遍历二叉树
void PostOrderTree(ptree root,void (*visit)(elemtype ))
{
	if(root)
	{
		PreOrderTree(root->lchild,visit);
		PreOrderTree(root->rchild,visit);
		(visit)(root->data);
	}
}

int main()
{
	ptree root = NULL;
	root = CreatTree();
	PreOrderTree(root,PrintResult);
	printf("\n");
	InOrderTree(root,PrintResult);
	printf("\n");
	PostOrderTree(root,PrintResult);
	printf("\n");
	return 0;
}

不过二叉树的建立方式各异，下面是第二种二叉树的建立方式

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define maxitem 1024
#define ok 1
typedef char elemtype;
typedef struct BiTNode
{
	elemtype data;
	struct BiTNode *lchild,*rchild;
}bitnode,*bitree;

//初始化树根节点
int init(bitree *t)
{
	*t = NULL;
	return ok;
}

//前序创建二叉树
int creat(bitree *t)
{
	char ch;
	scanf("%c",&ch);

		if (ch == '#')
			*t = NULL;
		else
		{
			*t = (bitree)malloc(sizeof(bitnode));
			if (!*t)
				exit(1);

			(*t)->data = ch;
			creat(&(*t)->lchild);creat(&(*t)->rchild);
		}

	return 1;
}

//前序遍历二叉树
void InOrderTraverse(bitree T)
{
	if(T)
	{
		InOrderTraverse(T->lchild);
		InOrderTraverse(T->rchild);
		printf("%c",T->data);
	}
}
int main()
{
	bitree t;
	init(&t);
	creat(&t);
	InOrderTraverse(t);
	printf("\n");
	return 0;
}