目录
前言
二叉树的遍历
模拟实现二叉树(链式二叉树)
前序遍历
前序遍历的实现
二叉树的递归遍历图
中序遍历
中序遍历的实现
后序遍历
后序遍历的实现
整体代码
前言
我们在二叉树的基本概念(C语言)中学习了二叉树的基本概念,现在我们开始学习二叉树的三种遍历方式的实现。
二叉树的遍历
- 前序遍历——访问根结点的操作发生在遍历其左右子树之前,即根->左->右
- 中序遍历——访问根结点的操作发生在遍历其左右子树之中,即左->根->右
- 后序遍历——访问根结点的操作发生在遍历其左右子树之后,即左->右->根
为了方便学习,我们将空的位置仍然以NULL表示
模拟实现二叉树(链式二叉树)
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
typedef int BTDataType;
typedef struct BinaryTreeNode
{
BTDataType data;
struct BinaryTreeNode* left;
struct BinaryTreeNode* right;
}TreeNode;
TreeNode* BuyTreeNode(int x)
{
TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
assert(node);
node->data = x;
node->left = NULL;
node->right = NULL;
return node;
}
TreeNode* CreatTree()
{
TreeNode* node1 = BuyTreeNode(1);
TreeNode* node2 = BuyTreeNode(2);
TreeNode* node3 = BuyTreeNode(3);
TreeNode* node4 = BuyTreeNode(4);
TreeNode* node5 = BuyTreeNode(5);
TreeNode* node6 = BuyTreeNode(6);
node1->left = node2;
node1->right = node4;
node2->left = node3;
//node2->right = NULL;
//node3->left = NULL;
//node3->right = NULL;
node4->left = node5;
node4->right = node6;
//node5->left = NULL;
//node5->right = NULL;
//node6->left = NULL;
//node6->right= NULL;
return node1;
}
int main()
{
TreeNode* root = CreatTree();
return 0;
}
前序遍历
前序遍历的实现
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
typedef int BTDataType;
typedef struct BinaryTreeNode
{
BTDataType data;
struct BinaryTreeNode* left;
struct BinaryTreeNode* right;
}TreeNode;
TreeNode* BuyTreeNode(int x)
{
TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
assert(node);
node->data = x;
node->left = NULL;
node->right = NULL;
return node;
}
TreeNode* CreatTree()
{
TreeNode* node1 = BuyTreeNode(1);
TreeNode* node2 = BuyTreeNode(2);
TreeNode* node3 = BuyTreeNode(3);
TreeNode* node4 = BuyTreeNode(4);
TreeNode* node5 = BuyTreeNode(5);
TreeNode* node6 = BuyTreeNode(6);
node1->left = node2;
node1->right = node4;
node2->left = node3;
//node2->right = NULL;
//node3->left = NULL;
//node3->right = NULL;
node4->left = node5;
node4->right = node6;
//node5->left = NULL;
//node5->right = NULL;
//node6->left = NULL;
//node6->right= NULL;
return node1;
}
void PrevOrder(TreeNode* root)
{
if(root == NULL)
{
printf("N ");
return;
}
printf("%d ", root->data);
PrevOrder(root->left);
PrevOrder(root->right);
}
int main()
{
TreeNode* root = CreatTree();
PrevOrder(root);
return 0;
}
实现步骤:
1、在完成一个二叉树的基础上,我们实现了前序遍历的理论变现,即根->左->右
2、先令前序遍历函数接收总根节点的值(单链表的头)
3、进入函数后判断此时的根节点(1)是否为空,若为空则打印N表示空,若不为空则打印对应的值(1)
4、此后递归的读取当前结点(1)的左子树的根节点(3),若该结点不为空则打印对应的值(3),然后继续递归读取其左子树的根节点(NULL),此时结点为空打印N后返回上一次的位置(3),然后执行当前结点(3)的右递归,当前结点的右子树的根节点(NULL)为空打印N后结束,返回上一次的位置(2)(到这里整个左子树最底层的一个PrevOrder已经结束了),然后执行当前结点(2)的右递归,当前结点的右子树的根节点(NULL)为空打印N后结束,返回上一次位置(1)(到这里整个左子树的倒数第二个PrevOrder已经结束了)
5、接下俩就应该去读取(1)的右子树的根节点(4)了(因为到这里第一个PrevOrder的左递归才算完全结束,现在开始右递归)
6、(4)不为空打印对应的值(4),然后继续递归读取其左子树的根节点(5),不为空打印对应的值(5),然后继续递归读取其左子树的根节点(NULL)为空打印N后返回上一次的位置(5),然后继续递归读取其右子树的根节点(NULL)为空打印N后返回上一次的位置(4)(到这里整个右子最底层的一个PrevOrder已经结束了)然后继续递归读取其右子树的根节点(6),不为空打印对应的值(6),然后继续递归读取其左子树的根节点(NULL)为空打印N后返回上一次的位置(6),然后继续递归读取其右子树的根节点(NULL)为空后打印N后返回上一次的位置(4)
7、至此,该二叉树的前序遍历完成
一共用了五次PrevOrder,左子树两次,右子树两次,主二叉树一次
二叉树的递归遍历图
中序遍历
中序遍历的实现
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
typedef int BTDataType;
typedef struct BinaryTreeNode
{
BTDataType data;
struct BinaryTreeNode* left;
struct BinaryTreeNode* right;
}TreeNode;
TreeNode* BuyTreeNode(int x)
{
TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
assert(node);
node->data = x;
node->left = NULL;
node->right = NULL;
return node;
}
TreeNode* CreatTree()
{
TreeNode* node1 = BuyTreeNode(1);
TreeNode* node2 = BuyTreeNode(2);
TreeNode* node3 = BuyTreeNode(3);
TreeNode* node4 = BuyTreeNode(4);
TreeNode* node5 = BuyTreeNode(5);
TreeNode* node6 = BuyTreeNode(6);
node1->left = node2;
node1->right = node4;
node2->left = node3;
//node2->right = NULL;
//node3->left = NULL;
//node3->right = NULL;
node4->left = node5;
node4->right = node6;
//node5->left = NULL;
//node5->right = NULL;
//node6->left = NULL;
//node6->right= NULL;
return node1;
}
void InOrder(TreeNode* root)
{
if (root == NULL)
{
printf("N ");
return;
}
InOrder(root->left);
printf("%d ", root->data);
InOrder(root->right);
}
int main()
{
TreeNode* root = CreatTree();
InOrder(root);
return 0;
}
实现步骤:中序遍历只是将前序遍历的PrevOrder中的 (root->data)与 (root->left)交换了位置,具体实现内容建议自行尝试
后序遍历
后序遍历的实现
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
typedef int BTDataType;
typedef struct BinaryTreeNode
{
BTDataType data;
struct BinaryTreeNode* left;
struct BinaryTreeNode* right;
}TreeNode;
TreeNode* BuyTreeNode(int x)
{
TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
assert(node);
node->data = x;
node->left = NULL;
node->right = NULL;
return node;
}
TreeNode* CreatTree()
{
TreeNode* node1 = BuyTreeNode(1);
TreeNode* node2 = BuyTreeNode(2);
TreeNode* node3 = BuyTreeNode(3);
TreeNode* node4 = BuyTreeNode(4);
TreeNode* node5 = BuyTreeNode(5);
TreeNode* node6 = BuyTreeNode(6);
node1->left = node2;
node1->right = node4;
node2->left = node3;
//node2->right = NULL;
//node3->left = NULL;
//node3->right = NULL;
node4->left = node5;
node4->right = node6;
//node5->left = NULL;
//node5->right = NULL;
//node6->left = NULL;
//node6->right= NULL;
return node1;
}
void LaterOrder(TreeNode* root)
{
if (root == NULL)
{
printf("N ");
return;
}
LaterOrder(root->left);
LaterOrder(root->right);
printf("%d ", root->data);
}
int main()
{
TreeNode* root = CreatTree();
LaterOrder(root);
printf("\n");
return 0;
}
注意事项:
1、建议多画图自己尝试一遍
2、搞懂此时的root是谁以及root->data到底打印的是谁的值,是完成三次遍历的基础
整体代码
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
typedef int BTDataType;
typedef struct BinaryTreeNode
{
BTDataType data;
struct BinaryTreeNode* left;
struct BinaryTreeNode* right;
}TreeNode;
TreeNode* BuyTreeNode(int x)
{
TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
assert(node);
node->data = x;
node->left = NULL;
node->right = NULL;
return node;
}
TreeNode* CreatTree()
{
TreeNode* node1 = BuyTreeNode(1);
TreeNode* node2 = BuyTreeNode(2);
TreeNode* node3 = BuyTreeNode(3);
TreeNode* node4 = BuyTreeNode(4);
TreeNode* node5 = BuyTreeNode(5);
TreeNode* node6 = BuyTreeNode(6);
node1->left = node2;
node1->right = node4;
node2->left = node3;
//node2->right = NULL;
//node3->left = NULL;
//node3->right = NULL;
node4->left = node5;
node4->right = node6;
//node5->left = NULL;
//node5->right = NULL;
//node6->left = NULL;
//node6->right= NULL;
return node1;
}
void PrevOrder(TreeNode* root)
{
if(root == NULL)
{
printf("N ");
return;
}
printf("%d ", root->data);
PrevOrder(root->left);
PrevOrder(root->right);
}
void InOrder(TreeNode* root)
{
if (root == NULL)
{
printf("N ");
return;
}
InOrder(root->left);
printf("%d ", root->data);
InOrder(root->right);
}
void LaterOrder(TreeNode* root)
{
if (root == NULL)
{
printf("N ");
return;
}
LaterOrder(root->left);
LaterOrder(root->right);
printf("%d ", root->data);
}
int main()
{
TreeNode* root = CreatTree();
PrevOrder(root);
printf("\n");
InOrder(root);
printf("\n");
LaterOrder(root);
printf("\n");
return 0;
}
~over~