（1）递归，层序遍历

（2）

BTree *createBinaryTree(char a[][10], int n) {
    if (strcmp(a[0], "null") == 0) {
        return NULL;
    }
    int i = 0;
    BTree *root = (struct node*)malloc(sizeof(struct node));
    strcpy(root->data, a[i++]);
    root->left = NULL;
    root->right = NULL;
    struct node** que = (struct node**)malloc(sizeof(struct node*));
    int front = 0, rear = 0;
    BTree *curr = root;
    que[rear++] = curr;
    while (front < rear && i < n) {
        curr = que[front++];
        for (int j = 0; j < 2 && i < n; j++, i++) {
            if (strcmp(a[i], "null") != 0) {
                if (j == 0) {
             ...