题目：

题解：

class Solution {
public:void addPath(vector<int> &vec, TreeNode *node) {int count = 0;while (node != nullptr) {++count;vec.emplace_back(node->val);node = node->right;}reverse(vec.end() - count, vec.end());}vector<int> postorderTraversal(TreeNode *root) {vector<int> res;if (root == nullptr) {return res;}TreeNode *p1 = root, *p2 = nullptr;while (p1 != nullptr) {p2 = p1->left;if (p2 != nullptr) {while (p2->right != nullptr && p2->right != p1) {p2 = p2->right;}if (p2->right == nullptr) {p2->right = p1;p1 = p1->left;continue;} else {p2->right = nullptr;addPath(res, p1->left);}}p1 = p1->right;}addPath(res, root);return res;}
};