c - 队列陷入无限循环的二叉树级顺序遍历

Question

我一直在尝试用 C 语言实现带队列的二叉树，我对这种语言还很陌生。我一直在尝试调试我用 C 编写的代码，从头开始编写代码但没有结果。我看不出我做错了什么。

我检查了我用整数数据编写的队列代码，它运行良好。

• 入队函数将一个元素压入队列
• dequeue 函数从队列中弹出一个元素
• 检查队列是否为空的空函数

然后我实现了二叉搜索树并打印了节点中的元素

root -> left -> left -> left -> data; //worked fine, was able to reach the extreme left leaf node

和

root -> right -> right -> right -> data;//工作正常，以防万一

还有一些像这样的遍历，看起来树形成得很好。我在 level_order() 函数中打印了队列，我能理解的是队列构建不正确。不知何故，整个事情进入了无限循环。我已经没有想法了。这是代码，谢谢。

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

struct BstNode{
    int data;
    struct BstNode *left;
    struct BstNode *right;
};

struct Queue{
    struct BstNode *address;
    struct Queue *next;
};

struct Queue *front = NULL;
struct Queue *back = NULL;

struct Queue* create_queue(BstNode **address){
    struct Queue *temp = (Queue*)malloc(sizeof(struct Queue));
    temp -> next = NULL;
    temp -> address = *address;
    return temp;
}

void enqueue(BstNode **address){
    struct Queue *temp = create_queue(address);
    if(front == NULL && back == NULL){
        front = back = temp;
    }
    else{
        temp -> next = back;
        back = temp;
    }
}

void dequeue(){
    if(front == NULL){
        return;
    }
    struct Queue* temp;
    temp = back;
    if(front == back){
        front = back = NULL;
    }
    else{
        back = back -> next;
    }
    free(temp);
}

bool empty(){
    if(front == NULL){
        return true;
    }
    return false;
}

void print_queue(){
    struct Queue *temp = back;
    while(temp != NULL){
        printf("%d", temp->address->data);
        temp = temp -> next;
    }
    printf("\n");
}

struct BstNode *root;

struct BstNode *create_node(int data){
    struct BstNode *temp = (BstNode *)malloc(sizeof(struct BstNode));
    temp -> data = data;
    temp -> left = NULL;
    temp -> right = NULL;
    return temp;
}

void insert_bst_cell(BstNode **node, int data){
    if((*node) == NULL){
        struct BstNode* temp = create_node(data);
        *node = temp;
    }
    else if(data > (*node)->data){
        insert_bst_cell(&(*node)->right, data);
    }
    else if(data < (*node)->data){
        insert_bst_cell(&(*node)->left, data);
    }
}

BstNode *first_element(){
    return front->address;
}

void level_order(){
    if(root == NULL) return;
    enqueue(&root);
    while(!(empty())){
        struct BstNode *current = first_element();
        dequeue();
        printf("%d\n", current->data);
        if(current->right != NULL){
            enqueue(&(current->left));
        }
        if(current->left != NULL){
            enqueue(&(current->right));
        }
    }
}

int main(int argc, char **argv)
{
    front = NULL;
    back = NULL;
    root = NULL;
    insert_bst_cell(&root, 15);
    insert_bst_cell(&root, 10);
    insert_bst_cell(&root, 20);
    insert_bst_cell(&root, 5);
    insert_bst_cell(&root, 11);
    insert_bst_cell(&root, 17);
    insert_bst_cell(&root, 25);
    insert_bst_cell(&root, 4);
    insert_bst_cell(&root, 6);
    insert_bst_cell(&root, 9);
    insert_bst_cell(&root, 12);
    insert_bst_cell(&root, 16);
    insert_bst_cell(&root, 19);
    insert_bst_cell(&root, 21);
    insert_bst_cell(&root, 35);
    level_order();
    return 0;
}

Answer 1

感谢Paul Georg Podlech指出我已经实现了一个堆栈而不是队列。另一个错误是

if(current->right != NULL){
    enqueue(&(current->left));
}
if(current->left != NULL){
    enqueue(&(current->right));
}

在此特定代码中。应该是

if(current->left != NULL){    //current -> right in previous snippet
    enqueue(&(current->left));  
}
if(current->right != NULL){    //current -> left in previous snippet
    enqueue(&(current->right));
}

以防万一我会发布工作代码

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

struct BstNode{
    int data;
    struct BstNode *left;
    struct BstNode *right;
};

struct Queue{
    struct BstNode *address;
    struct Queue *next;
};

struct Queue *front = NULL;
struct Queue *back = NULL;

struct Queue* create_queue(BstNode **address){
    struct Queue *temp = (Queue*)malloc(sizeof(struct Queue));
    temp -> next = NULL;
    temp -> address = *address;
    return temp;
}

void enqueue(BstNode **address){
    struct Queue *temp = create_queue(address);
    if(front == NULL && back == NULL){
        front = back = temp;
    }
    else{
//        temp -> next = back;
        back -> next = temp;
        back = temp;
    }
}

void dequeue(){
    if(front == NULL){
        return;
    }
    struct Queue* temp;
    temp = front;
    if(front == back){
        front = back = NULL;
    }
    else{
        front = front -> next;
    }
    free(temp);
}

bool empty(){
    if(front == NULL){
        return true;
    }
    return false;
}

void print_queue(){
    struct Queue *temp = back;
    while(temp != NULL){
        printf("%d", temp->address->data);
        temp = temp -> next;
    }
    printf("\n");
}

struct BstNode *root;

struct BstNode *create_node(int data){
    struct BstNode *temp = (BstNode *)malloc(sizeof(struct BstNode));
    temp -> data = data;
    temp -> left = NULL;
    temp -> right = NULL;
    return temp;
}

void insert_bst_cell(BstNode **node, int data){
    if((*node) == NULL){
        struct BstNode* temp = create_node(data);
        *node = temp;
    }
    else if(data > (*node)->data){
        insert_bst_cell(&(*node)->right, data);
    }
    else if(data < (*node)->data){
        insert_bst_cell(&(*node)->left, data);
    }
}

BstNode *first_element(){
    return front->address;
}

void level_order(){
    if(root == NULL) return;
    enqueue(&root);
    while(!(empty())){
        struct BstNode *current = first_element();
        dequeue();
        printf("%d\n", current->data);
        if(current->left != NULL){
            enqueue(&(current->left));
        }
        if(current->right != NULL){
            enqueue(&(current->right));
        }
    }
}

int main(int argc, char **argv)
{
    front = NULL;
    back = NULL;
    root = NULL;
    insert_bst_cell(&root, 15);
    insert_bst_cell(&root, 10);
    insert_bst_cell(&root, 20);
    insert_bst_cell(&root, 5);
    insert_bst_cell(&root, 11);
    insert_bst_cell(&root, 17);
    insert_bst_cell(&root, 25);
    insert_bst_cell(&root, 4);
    insert_bst_cell(&root, 6);
    insert_bst_cell(&root, 9);
    insert_bst_cell(&root, 12);
    insert_bst_cell(&root, 16);
    insert_bst_cell(&root, 19);
    insert_bst_cell(&root, 21);
    insert_bst_cell(&root, 35);
    level_order();
    return 0;
}

感谢大家的宝贵时间和意见。