C语言【问题描述】 按层序遍历打印二叉树。(队列操作采用循环队列） 【输入形式】 二叉树的先序扩展序列（字符串，以#填充空白结点） 【输出形式】 层序遍历打印二叉树 【样例输入】 image.png ABC##DE#G##F### 【样例输出】 ABCDEFG

以下是C语言的代码实现，使用循环队列来实现二叉树的层序遍历：

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

#define MAXSIZE 100

typedef struct TreeNode {
    char data;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode, *Tree;

typedef struct Queue {
    TreeNode *data[MAXSIZE];
    int front, rear;
} Queue;

// 初始化队列
void initQueue(Queue *q) {
    q->front = 0;
    q->rear = 0;
}

// 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 + 1) % MAXSIZE == q->front) {
        printf("Queue is full.\n");
        return;
    }
    q->data[q->rear] = node;
    q->rear = (q->rear + 1) % MAXSIZE;
}

// 出队
TreeNode *dequeue(Queue *q) {
    if (isEmpty(q)) {
        printf("Queue is empty.\n");
        return NULL;
    }
    TreeNode *node = q->data[q->front];
    q->front = (q->front + 1) % MAXSIZE;
    return node;
}

// 创建二叉树
Tree createTree() {
    char c;
    scanf("%c", &c);
    if (c == '#') {
        return NULL;
    }
    Tree tree = (Tree)malloc(sizeof(TreeNode));
    tree->data = c;
    tree->left = createTree();
    tree->right = createTree();
    return tree;
}

// 层序遍历
void levelTraversal(Tree tree) {
    if (tree == NULL) {
        return;
    }
    Queue q;
    initQueue(&q);
    enqueue(&q, tree);
    while (!isEmpty(&q)) {
        TreeNode *node = dequeue(&q);
        printf("%c", node->data);
        if (node->left != NULL) {
            enqueue(&q, node->left);
        }
        if (node->right != NULL) {
            enqueue(&q, node->right);
        }
    }
}

int main() {
    Tree tree = NULL;
    printf("Please input the preorder sequence of the binary tree: ");
    tree = createTree();
    printf("The level order traversal of the binary tree is: ");
    levelTraversal(tree);
    printf("\n");
    return 0;
}

输入样例：

ABC##DE#G##F###

输出样例：

The level order traversal of the binary tree is: ABCDEFG