C语言求取二叉树每层结点的个数

下面是C语言实现二叉树每层结点个数的代码：

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

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

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

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

// 创建二叉树节点
TreeNode* createNode(int val) {
    TreeNode *node = (TreeNode*) malloc(sizeof(TreeNode));
    node->val = val;
    node->left = NULL;
    node->right = NULL;
    return node;
}

// 向队列中添加元素
void enqueue(Queue *q, TreeNode *node) {
    QueueNode *qNode = (QueueNode*) malloc(sizeof(QueueNode));
    qNode->node = node;
    qNode->next = NULL;
    if (q->rear == NULL) {
        q->front = q->rear = qNode;
    } else {
        q->rear->next = qNode;
        q->rear = qNode;
    }
}

// 从队列中删除元素
TreeNode* dequeue(Queue *q) {
    if (q->front == NULL) {
        return NULL;
    } else {
        QueueNode *node = q->front;
        TreeNode *tnode = node->node;
        q->front = q->front->next;
        free(node);
        if (q->front == NULL) {
            q->rear = NULL;
        }
        return tnode;
    }
}

// 获取二叉树每层节点数量
int* levelOrder(TreeNode *root, int *returnSize) {
    int *res = (int*) malloc(sizeof(int) * 1000);
    int level = 0, count = 0;
    Queue *queue = (Queue*) malloc(sizeof(Queue));
    queue->front = queue->rear = NULL;
    enqueue(queue, root);
    while (queue->front != NULL) {
        level++;
        count = 0;
        int n = queue->rear - queue->front + 1;
        for (int i = 0; i < n; i++) {
            TreeNode *node = dequeue(queue);
            if (node != NULL) {
                count++;
                if (node->left != NULL) {
                    enqueue(queue, node->left);
                }
                if (node->right != NULL) {
                    enqueue(queue, node->right);
                }
            }
        }
        res[level - 1] = count;
    }
    *returnSize = level;
    return res;
}

int main() {
    TreeNode *node1 = createNode(3);
    TreeNode *node2 = createNode(9);
    TreeNode *node3 = createNode(20);
    TreeNode *node4 = createNode(15);
    TreeNode *node5 = createNode(7);
    TreeNode *node6 = createNode(8);
    TreeNode *node7 = createNode(10);
    node1->left = node2;
    node1->right = node3;
    node3->left = node4;
    node3->right = node5;
    node4->left = node6;
    node5->right = node7;
    int size = 0;
    int *res = levelOrder(node1, &size);
    for (int i = 0; i < size; i++) {
        printf("%d ", res[i]);
    }
    free(res);
    return 0;
}

该代码实现了二叉树的遍历，使用队列将每个结点加入队列，并在出队的过程中统计每层的结点数量，最终得到每层的结点数量并返回。