单选题库

TreeNode* op(TreeNode* root, int val) {
    if (root == nullptr) return new TreeNode(val);
    if (val < root->val) {
        root->left = op(root->left, val);
    } else {
        root->right = op(root->right, val);
    }
    return root;
}

bool isCompleteTree(TreeNode* root) {
    if (root == nullptr) return true;
    queue<TreeNode*> q;
    q.push(root);
    bool hasNull = false;
    while (!q.empty()) {
        TreeNode* node = q.front();
        q.pop();
        if (node == nullptr) {
            hasNull = true;
        } else {
            if (hasNull) return false;
            q.push(node->left);
            q.push(node->right);
        }
    }
    return true;
}

void traverse(TreeNode* root) {
    if (root == nullptr) return;
    cout << root->val << " ";
    traverse(root->left);
    traverse(root->right);
}