// Author: btjanaka (Bryon Tjanaka)

// Problem: (Leetcode) 144

// Title: Binary Tree Preorder Traversal

// Link: https://leetcode.com/problems/binary-tree-preorder-traversal

// Idea:

// Difficulty: medium

// Tags: binary-tree, implementation

/**

* Definition for a binary tree node.

* struct TreeNode {

* int val;

* TreeNode *left;

* TreeNode *right;

* TreeNode(int x) : val(x), left(NULL), right(NULL) {}

* };

*/

class Solution {

public:

vector<int> preorderTraversal(TreeNode* root) {

vector<int> res;

stack<TreeNode*> to_visit;

if (root != nullptr) to_visit.push(root);

while (to_visit.size() > 0) {

TreeNode* curr = to_visit.top();

to_visit.pop();

res.push_back(curr->val);

if (curr->right != nullptr) {

to_visit.push(curr->right);

}

if (curr->left != nullptr) {

to_visit.push(curr->left);

}

}

return res;

}

};