利用队列，编程实现二叉树的层次遍历。 输入格式： 一个字符序列，表示空子树处为*号的二叉树的先序遍历序列。C语言 输出格式： 一个字符序列，表示二叉树的层次遍历序列。输入样例： abd*f***ce*** 输出样例： abcdef

好的，以下是 C 代码实现：

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

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

TreeNode* buildTree(char** preorder) {
    char* val = *preorder;
    (*preorder)++;
    if (*val == '*' || *val == '\0') {
        return NULL;
    }
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = *val;
    root->left = buildTree(preorder);
    root->right = buildTree(preorder);
    return root;
}

void levelOrder(TreeNode* root) {
    if (!root) {
        return;
    }
    TreeNode** queue = (TreeNode**)malloc(sizeof(TreeNode*) * 100);
    int front = 0, rear = 0;
    queue[rear++] = root;
    while (front < rear) {
        int size = rear - front;
        for (int i = 0; i < size; i++) {
            TreeNode* node = queue[front++];
            printf("%c", node->val);
            if (node->left) {
                queue[rear++] = node->left;
            }
            if (node->right) {
                queue[rear++] = node->right;
            }
        }
    }
}

int main() {
    char preorder[100];
    scanf("%s", preorder);
    char* p = preorder;
    TreeNode* root = buildTree(&p);
    levelOrder(root);
    return 0;
}

输入示例：

abd*f***ce***

输出示例：

abcdef