/* struct TreeNode { int val; struct TreeNode *left; struct TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) { } }; */ class Solution { public: string req; char* Serialize(TreeNode *root) { if(root == nullptr) return nullptr;// 如果根节点为空就返回空指针 queue<TreeNode *> q; if(root != nu...