使用c语言实现层序输出二叉树

下面是使用C语言实现层序遍历二叉树的代码：

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

// 二叉树结构体
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

// 队列结构体
struct Queue {
    struct TreeNode **nodes;
    int head;
    int tail;
    int size;
};

// 创建队列
struct Queue* createQueue(int size)
{
    struct Queue *queue = (struct Queue*) malloc(sizeof(struct Queue));
    queue->nodes = (struct TreeNode**) malloc(size * sizeof(struct TreeNode*));
    queue->head = 0;
    queue->tail = 0;
    queue->size = size;

    return queue;
}

// 入队
void enqueue(struct Queue *queue, struct TreeNode *node)
{
    queue->nodes[queue->tail++] = node;
}

// 出队
struct TreeNode* dequeue(struct Queue *queue)
{
    return queue->nodes[queue->head++];
}

// 判断队列是否为空
int isEmpty(struct Queue *queue)
{
    return queue->head == queue->tail;
}

// 层序遍历二叉树
void levelOrder(struct TreeNode* root) {
    if (!root) {
        return;
    }

    struct Queue *queue = createQueue(100);
    enqueue(queue, root);

    while (!isEmpty(queue)) {
        int size = queue->tail - queue->head;
        for (int i = 0; i < size; i++) {
            struct TreeNode *node = dequeue(queue);
            printf("%d ", node->val);

            if (node->left) {
                enqueue(queue, node->left);
            }

            if (node->right) {
                enqueue(queue, node->right);
            }
        }
        printf("\n");
    }
}

// 测试代码
int main() {
    struct TreeNode *root = (struct TreeNode*) malloc(sizeof(struct TreeNode));
    root->val = 1;

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

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

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

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

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

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

    levelOrder(root);

    return 0;
}

输出结果为：

1 
2 3 
4 5 6 7 

可以看到，该代码实现了层序遍历二叉树，并按层输出二叉树结点的值。