请用c语言实现二叉树的层序遍历完整代码

首先，我们需要定义二叉树的结构体：

typedef struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode;

然后，我们定义一个队列，用于层序遍历时保存每一层的节点：

typedef struct QueueNode {
    TreeNode *data;
    struct QueueNode *next;
} QueueNode;

typedef struct Queue {
    QueueNode *front;
    QueueNode *rear;
    int size;
} Queue;

接下来是二叉树的层序遍历函数：

void levelOrder(TreeNode *root) {
    if (!root) return;

    Queue *q = (Queue *)malloc(sizeof(Queue));
    q->front = q->rear = NULL;
    q->size = 0;

    // 先将根节点入队
    QueueNode *node = (QueueNode *)malloc(sizeof(QueueNode));
    node->data = root;
    node->next = NULL;
    q->front = q->rear = node;
    q->size++;

    while (q->size > 0) {
        int level_size = q->size;
        for (int i = 0; i < level_size; i++) {
            // 出队并打印
            TreeNode *cur = q->front->data;
            printf("%d ", cur->val);
            q->front = q->front->next;
            q->size--;

            // 左右子节点入队
            if (cur->left) {
                QueueNode *new_node = (QueueNode *)malloc(sizeof(QueueNode));
                new_node->data = cur->left;
                new_node->next = NULL;
                q->rear->next = new_node;
                q->rear = new_node;
                q->size++;
            }
            if (cur->right) {
                QueueNode *new_node = (QueueNode *)malloc(sizeof(QueueNode));
                new_node->data = cur->right;
                new_node->next = NULL;
                q->rear->next = new_node;
                q->rear = new_node;
                q->size++;
            }
        }
        printf("\n");
    }
}

完整代码如下：