/** * struct TreeNode { * int val; * struct TreeNode *left; * struct TreeNode *right; * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {} * }; */ class Solution { public: vector<int> ans; //递归法 void LRD(TreeNode* cur){ if(!cur) return; LRD(cur->left); LRD(cur->right); ans.push_b...