二叉树的层次遍历的C++代码

以下是二叉树层次遍历的C代码：

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

//定义树节点的结构体
typedef struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode;

//定义队列节点的结构体
typedef struct QueueNode {
    TreeNode *treenode;
    struct QueueNode *next;
} QueueNode;

//初始化队列
QueueNode* initQueue() {
    QueueNode *head = (QueueNode *) malloc(sizeof(QueueNode));
    head->next = NULL;
    return head;
}

//入队
void enqueue(QueueNode *head, TreeNode *treenode) {
    QueueNode *p = head;
    while (p->next != NULL) {
        p = p->next;
    }
    QueueNode *q = (QueueNode *) malloc(sizeof(QueueNode));
    q->treenode = treenode;
    q->next = NULL;
    p->next = q;
}

//出队
TreeNode* dequeue(QueueNode *head) {
    if (head->next == NULL) {
        return NULL;
    }
    QueueNode *p = head->next;
    TreeNode *treenode = p->treenode;
    head->next = p->next;
    free(p);
    return treenode;
}

//层次遍历方法
void levelTraversal(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    QueueNode *queue = initQueue();
    enqueue(queue, root);
    while (queue->next != NULL) {
        TreeNode *treenode = dequeue(queue);
        printf("%d ", treenode->val);
        if (treenode->left != NULL) {
            enqueue(queue, treenode->left);
        }
        if (treenode->right != NULL) {
            enqueue(queue, treenode->right);
        }
    }
}

int main() {
    // 创建二叉树
    TreeNode *root = (TreeNode *) malloc(sizeof(TreeNode));
    root->val = 1;

    root->left = (TreeNode *) malloc(sizeof(TreeNode));
    root->left->val = 2;

    root->right = (TreeNode *) malloc(sizeof(TreeNode));
    root->right->val = 3;

    root->left->left = (TreeNode *) malloc(sizeof(TreeNode));
    root->left->left->val = 4;

    root->left->right = (TreeNode *) malloc(sizeof(TreeNode));
    root->left->right->val = 5;

    root->right->left = (TreeNode *) malloc(sizeof(TreeNode));
    root->right->left->val = 6;

    root->right->right = (TreeNode *) malloc(sizeof(TreeNode));
    root->right->right->val = 7;

    // 层次遍历
    levelTraversal(root);

    return 0;
}

该代码可以实现二叉树的层次遍历，使用队列作为辅助数据结构，遍历时按照层次顺序出队并访问队首元素，然后将它的左右子树分别入队。