二叉树的深度优先遍历主要有三种:
前序:根左右
中序:左根右
后序:左右根
下面是完整的实现和讲解:
#include <stdio.h>
#include <stdlib.h>
/*二叉树的深度遍历:
* 例如二叉树
* 1
* / \
* 2 3
* /\
* 4 5
* 中序遍历:左根右 4-2-5-1-3
* 前序遍历:根左右 1-2-4-5-3
* 后序遍历:左右根 4-5-2-3-1
*
* 然而它的BFS(广度)或者水平层次遍历:1-2-3-4-5
*
*/
/*二叉树构造*/
struct node {
int data;
struct node *left;
struct node *right;
};
/*通过给定值,构造一颗二叉树,它的左右指针为NULL*/
struct node *newNode(int data) {
//一说到要构造二叉树,就要相当要申请内存
struct node *node = (struct node *) malloc(sizeof(struct node));
node->data = data;
node->left = NULL;
node->right = NULL;
return node;
}
/*中序遍历:左根右*/
void printInorder(struct node *node) {
if (node == NULL){
return;
}
//在递归的时候,如果node为null,例如node->left为NULL,printInorder(node->left)这个就没有任何输出
//会继续执行下一句,printf("%d ",node->data);
//遍历左子树
printInorder(node->left);
//遍历根结点
printf("%d ",node->data);
//遍历右子树
printInorder(node->right);
}
/*前序遍历:根左右*/
void printPreorder(struct node* node){
if (node == NULL){
return;
}
//遍历根结点
printf("%d ",node->data);
//遍历左子树
printPreorder(node->left);
//遍历右子树
printPreorder(node->right);
}
//后序遍历:左右根
void printPostorder(struct node* node)
{
if (node == NULL)
return;
// first recur on left subtree
printPostorder(node->left);
// then recur on right subtree
printPostorder(node->right);
// now deal with the node
printf("%d ", node->data);
}
int main() {
//构造树
//构造根节点
struct node *root = newNode(1);
root->left = newNode(2);
root->right = newNode(3);
root->left->left = newNode(4);
root->left->right = newNode(5);
printf("\nPreorder traversal of binary tree is \n");
printPreorder(root);//1 2 4 5 3
printf("\nInorder traversal of binary tree is \n");
printInorder(root);//4 2 5 1 3
printf("\nPostorder traversal of binary tree is \n");
printPostorder(root);//4 5 2 3 1
return 0;
}
DFS三种遍历方式,采用递归的方式,相对来说比较好理解一些。