/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> my_stack;
        if(root == nullptr) return result;
        my_stack.push(root);
        while(my_stack.empty() != 1)
        {
            TreeNode* my_node = my_stack.top();
            my_stack.pop();
            //和前序一样，但是变成中右左
            result.push_back(my_node->val);
            if(my_node->left != nullptr) my_stack.push(my_node->left);
            if(my_node->right != nullptr) my_stack.push(my_node->right);  
        }
    //反转，变成左右中
        reverse (result.begin() , result.end());
        return result;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> my_stack;
        if(root == nullptr) return result;
        TreeNode* cur = root;
        while(cur != nullptr || my_stack.empty() != 1)
        {
            if(cur != nullptr)//找到cur的最左叶子节点
            {
                my_stack.push(cur);//找的过程中所有的左节点都存起来
                cur = cur->left;
            }else//处理中节点和右节点
            {
                cur = my_stack.top();//输出栈里之前存的左节点 ，这时左节点看作成中间节点
                my_stack.pop();
                result.push_back(cur->val);
                cur = cur->right;//然后找刚才输出左节点作为中间点时的右节点
            }
        }       
        return result;
    }
};