用c语言写一个用层序遍历输入的二叉树

可以使用队列来实现二叉树的层序遍历。具体步骤如下：

1. 定义一个队列，将根节点入队。
2. 当队列不为空时，取出队首元素，输出该节点的值，并将其左右子节点入队。
3. 重复步骤2，直到队列为空。

以下是示例代码：

#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;

void initQueue(Queue *q) {
    q->front = q->rear = NULL;
}

int isEmpty(Queue *q) {
    return q->front == NULL;
}

void enqueue(Queue *q, TreeNode *node) {
    QueueNode *newNode = (QueueNode *)malloc(sizeof(QueueNode));
    newNode->node = node;
    newNode->next = NULL;
    if (isEmpty(q)) {
        q->front = q->rear = newNode;
    } else {
        q->rear->next = newNode;
        q->rear = newNode;
    }
}

TreeNode *dequeue(Queue *q) {
    if (isEmpty(q)) {
        return NULL;
    }
    TreeNode *node = q->front->node;
    QueueNode *temp = q->front;
    q->front = q->front->next;
    free(temp);
    if (q->front == NULL) {
        q->rear = NULL;
    }
    return node;
}

TreeNode *buildTree(int *arr, int size, int index) {
    if (index >= size || arr[index] == -1) {
        return NULL;
    }
    TreeNode *root = (TreeNode *)malloc(sizeof(TreeNode));
    root->val = arr[index];
    root->left = buildTree(arr, size, 2 * index + 1);
    root->right = buildTree(arr, size, 2 * index + 2);
    return root;
}

void levelOrder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    Queue q;
    initQueue(&q);
    enqueue(&q, root);
    while (!isEmpty(&q)) {
        TreeNode *node = dequeue(&q);
        printf("%d ", node->val);
        if (node->left != NULL) {
            enqueue(&q, node->left);
        }
        if (node->right != NULL) {
            enqueue(&q, node->right);
        }
    }
}

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6, 7, -1, -1, -1, -1, -1, -1, -1, -1};
    int size = sizeof(arr) / sizeof(arr[]);
    TreeNode *root = buildTree(arr, size, );
    levelOrder(root);
    return ;
}