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Binary Tree Postorder Traversal

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Description

https://leetcode.com/problems/binary-tree-postorder-traversal/description/

Solution

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Node {
public:
    bool l;
    bool r;
    TreeNode* treeNode; 
    Node(TreeNode* node) {
        this->treeNode = node;
        this->l = false;
        this->r = false;
    }
};

class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> ret;
        stack<Node*> s;
        Node* start = new Node(root);
        if (root == NULL) return ret;
        s.push(start);
        while (s.empty() == false) {
            Node* currentNode = s.top();
            if (currentNode->l == false && currentNode->treeNode->left != NULL) {
                currentNode->l = true;
                TreeNode* traverse = currentNode->treeNode->left;
                while(traverse != NULL) {
                    Node* newNode = new Node(traverse);
                    newNode->l = true;
                    s.push(newNode);
                    traverse = traverse->left;
                }
                continue;
            }
            if (currentNode->r == true || currentNode->treeNode->right == NULL) {
                s.pop();
                ret.push_back(currentNode->treeNode->val);
                continue;
            }
            //Default case, find the node in the right subtree.
            currentNode->r = true;
            s.push(new Node(currentNode->treeNode->right));
        }
        return ret;
    }
};