樹遍歷

前序遍歷

這是一個簡單的三個步驟。

• 訪問根結點
• 遍歷左子樹
• 遍歷右子樹

void preOrder(struct node* root){
if(root != NULL){
printf("%d ",root->data);
preOrder(root->leftChild);
preOrder(root->rightChild);
}
}

中序遍歷

這是一個簡單的三個步驟。

• 遍歷左子樹
• 訪問根結點
• 遍歷右子樹

void inOrder(struct node* root){
if(root != NULL){
inOrder(root->leftChild);
printf("%d ",root->data);
inOrder(root->rightChild);
}
}

後序遍歷

這是一個簡單的三個步驟。

• 遍歷左子樹
• 遍歷右子樹
• 訪問根結點

void postOrder(struct node* root){
if(root != NULL){
postOrder(root->leftChild);
postOrder(root->rightChild);
printf("%d ",root->data);
}
}

演示程序

TreeDemo.c

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

struct node {
int data;
struct node *leftChild;
struct node *rightChild;
};

struct node *root = NULL;

void insert(int data){
struct node *tempNode = (struct node*) malloc(sizeof(struct node));
struct node *current;
struct node *parent;

tempNode->data = data;
tempNode->leftChild = NULL;
tempNode->rightChild = NULL;

//if tree is empty
if(root == NULL){
root = tempNode;
}else{
current = root;
parent = NULL;

  while(1){                
     parent = current;
     //go to left of the tree
     if(data < parent->data){
        current = current->leftChild;                
        //insert to the left
        if(current == NULL){
           parent->leftChild = tempNode;
           return;
        }
     }//go to right of the tree
     else{
        current = current->rightChild;
        //insert to the right
        if(current == NULL){
           parent->rightChild = tempNode;
           return;
        }
     }
  }            

}
}

struct node* search(int data){
struct node *current = root;
printf("Visiting elements: ");

while(current->data != data){
if(current != NULL)
printf("%d ",current->data);

     //go to left tree
     if(current->data > data){
        current = current->leftChild;
     }//else go to right tree
     else{                
        current = current->rightChild;
     }

     //not found
     if(current == NULL){
        return NULL;
     }
  }

return current;
}

void preOrder(struct node* root){
if(root != NULL){
printf("%d ",root->data);
preOrder(root->leftChild);
preOrder(root->rightChild);
}
}

void inOrder(struct node* root){
if(root != NULL){
inOrder(root->leftChild);
printf("%d ",root->data);
inOrder(root->rightChild);
}
}

void postOrder(struct node* root){
if(root != NULL){
postOrder(root->leftChild);
postOrder(root->rightChild);
printf("%d ",root->data);
}
}

void traverse(int traversalType){
switch(traversalType){
case 1:
printf("\nPreorder traversal: ");
preOrder(root);
break;
case 2:
printf("\nInorder traversal: ");
inOrder(root);
break;
case 3:
printf("\nPostorder traversal: ");
postOrder(root);
break;
}
}

int main() {
/* 11 //Level 0
*/
insert(11);

/* 11 //Level 0
* |
* |---20 //Level 1
*/
insert(20);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
*/
insert(3);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* |
* |--42 //Level 2
*/
insert(42);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* |
* |--42 //Level 2
* |
* |--54 //Level 3
*/
insert(54);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* |
* 16--|--42 //Level 2
* |
* |--54 //Level 3
*/
insert(16);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* |
* 16--|--42 //Level 2
* |
* 32--|--54 //Level 3
*/
insert(32);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* | |
* |--9 16--|--42 //Level 2
* |
* 32--|--54 //Level 3
*/
insert(9);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* | |
* |--9 16--|--42 //Level 2
* | |
* 4--| 32--|--54 //Level 3
*/
insert(4);

/* 11 //Level 0
* |
* 3---|---20 //Level 1
* | |
* |--9 16--|--42 //Level 2
* | |
* 4--|--10 32--|--54 //Level 3
*/
insert(10);

struct node * temp = search(32);
if(temp != NULL){
printf("Element found.\n");
printf("( %d )",temp->data);
printf("\n");
}else{
printf("Element not found.\n");
}

struct node *node1 = search(2);
if(node1 != NULL){
printf("Element found.\n");
printf("( %d )",node1->data);
printf("\n");
}else{
printf("Element not found.\n");
}

//pre-order traversal
//root, left ,right
traverse(1);

//in-order traversal
//left, root ,right
traverse(2);

//post order traversal
//left, right, root
traverse(3);
}

如果我們編譯並運行上述程序，那麼這將產生以下結果 -

Visiting elements: 11 20 42 Element found.(32)
Visiting elements: 11 3 Element not found.

Preorder traversal: 11 3 9 4 10 20 16 42 32 54
Inorder traversal: 3 4 9 10 11 16 20 32 42 54
Postorder traversal: 4 10 9 3 16 32 54 42 20 11