Three traversal methods of binary tree

  Catalog

1. The structure of a binary tree ：

2. Preorder traversal of two tree ：

3. Middle order traversal of binary trees ：

4. Postorder traversal of binary trees ：

5. Before the binary tree 、 in 、 Code implementation of post order ：

Preorder traversal function ：

  Middle order ergodic function ：

  After the sequence traversal ：

Complete code ： 

Screenshot of code running result ：

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1. The structure of a binary tree ：

Each binary tree can be divided into three parts ：1. The root node 2. The left subtree 3. Right subtree .

Like the one above A The left and right subtrees of are B、C, and E The left and right subtrees of are NULL、NULL. Usually we put NULL Omit .

2. Preorder traversal of two tree ：

Also called root first traversal , The traversal order is the root node 、 The left subtree 、 Right subtree .

Preorder traversal in the figure above ：A B D NULL NULL E NULL NULL C NULL NULL

Omit NULL after ：A B D E C

3. Middle order traversal of binary trees ：

traversal order ： The left subtree 、 The root node 、 Right subtree

The middle order traversal in the figure above ：NULL D NULL B NULL E NULL A NULL C NULL

Omit NULL after ：D B E A C

4. Postorder traversal of binary trees ：

traversal order ： The left subtree 、 Right subtree 、 The root node

The middle order traversal in the figure above ：NULL NULL D NULL NULL E B NULL NULL C A

Omit NULL after ：D E B C A

5. Before the binary tree 、 in 、 Code implementation of post order ：

Preorder traversal function ：

void prev_order(BTNode* root)// The former sequence traversal 
{
	if (root == NULL)
	{
		printf("NULL");
		return;
	}
	printf("%c ", root->data);
	prev_order(root->left);
	prev_order(root->right);
}

  Middle order ergodic function ：

void on_order(BTNode* root)// In the sequence traversal 
{
	if (root == NULL)
	{
		printf("NULL\n");
		return;
	}
	prev_order(root->left);
	printf("%c ", root->data);
	prev_order(root->right);
}

  After the sequence traversal ：

void post_order(BTNode* root)// After the sequence traversal 
{
	if (root == NULL)
	{
		printf("  NULL   \n");
		return;
	}
	prev_order(root->left);
	prev_order(root->right);
	printf("%c    ", root->data);
}

Complete code ： 

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
typedef char BTDataType;
typedef struct BinaryTreeNode
{
	BTDataType data;
	struct BinaryTreeNode* left;
	struct BinaryTreeNode* right;
}BTNode;
BTNode* BuyNode(BTDataType x)// Open up space to store variables 
{
	BTNode* newnode = (BTNode*)malloc(sizeof(BTNode));
	newnode->data = x;
	newnode->left = NULL;
	newnode->right = NULL;
	return newnode;
}
void prev_order(BTNode* root)// The former sequence traversal 
{
	if (root == NULL)
	{
		printf("NULL");
		return;
	}
	printf("%c ", root->data);
	prev_order(root->left);
	prev_order(root->right);
}
void on_order(BTNode* root)// In the sequence traversal 
{
	if (root == NULL)
	{
		printf("NULL\n");
		return;
	}
	prev_order(root->left);
	printf("%c ", root->data);
	prev_order(root->right);
}
void post_order(BTNode* root)// After the sequence traversal 
{
	if (root == NULL)
	{
		printf("  NULL   \n");
		return;
	}
	prev_order(root->left);
	prev_order(root->right);
	printf("%c    ", root->data);
}
int main(void)
{
	BTNode* n1 = BuyNode('A');
	BTNode* n2 = BuyNode('B');
	BTNode* n3 = BuyNode('C');
	BTNode* n4 = BuyNode('D');
	BTNode* n5 = BuyNode('E');
	n1->left = n2;
	n1->right = n3;
	n2->left = n4;
	n2->right = n5;
	prev_order(n1);
	printf("\n");
	on_order(n1);
	printf("\n");
	post_order(n1);
	printf("\n");
	return 0;
}

Screenshot of code running result ：

When learning data structure , Many of us don't know where to start , I don't know how to consolidate my knowledge , Today, I would like to recommend a website that I think is particularly excellent ： Cattle from , There are a lot of algorithm questions and interview questions ,
link ： Cattle from YYDS