二叉树的层次遍历，用c语言实现

二叉树的层次遍历是一种广度优先搜索算法，它按照从上到下、从左到右的顺序遍历二叉树的所有节点。下面是用C语言实现二叉树的层次遍历的代码：

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

// 定义二叉树节点结构体
typedef struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode;

// 定义队列结构体
typedef struct Queue {
    TreeNode **data;
    int front;
    int rear;
    int size;
} Queue;

// 初始化队列
Queue *initQueue(int size) {
    Queue *q = (Queue *)malloc(sizeof(Queue));
    q->data = (TreeNode **)malloc(sizeof(TreeNode *) * size);
    q->front = 0;
    q->rear = 0;
    q->size = size;
    return q;
}

// 判断队列是否为空
int isEmpty(Queue *q) {
    return q->front == q->rear;
}

// 入队
void enqueue(Queue *q, TreeNode *node) {
    if (q->rear == q->size) {
        printf("Queue is full.\n");
        return;
    }
    q->data[q->rear++] = node;
}

// 出队
TreeNode *dequeue(Queue *q) {
    if (isEmpty(q)) {
        printf("Queue is empty.\n");
        return NULL;
    }
    return q->data[q->front++];
}

// 层次遍历
void levelOrder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    Queue *q = initQueue(100);
    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);
        }
    }
}

// 创建二叉树
TreeNode *createTree() {
    int val;
    scanf("%d", &val);
    if (val == -1) {
        return NULL;
    }
    TreeNode *node = (TreeNode *)malloc(sizeof(TreeNode));
    node->val = val;
    node->left = createTree();
    node->right = createTree();
    return node;
}

int main() {
    TreeNode *root = createTree();
    printf("Level order traversal: ");
    levelOrder(root);
    printf("\n");
    return 0;
}