Given a binary tree. Find the preorder traversal of the tree without using recursion.

Example 1:

Input:
           1
         /   \
        2     3
      /  \
     4    5
Output: 1 2 4 5 3
Explanation:
Preorder traversal (Root->Left->Right) of 
the tree is 1 2 4 5 3.

Example 2

Input:
            8
          /   \
         1      5
          \    /  \
           7  10   6
            \  /
            10 6
Output: 8 1 7 10 5 10 6 6 
Explanation:
Preorder traversal (Root->Left->Right) 
of the tree is 8 1 7 10 5 10 6 6.

Your task:

You don't need to read input or print anything. Your task is to complete the function preOrder() which takes the root of the tree as input and returns a list containing the preorder traversal of the tree, calculated without using recursion.

Expected time complexity: O(N)
Expected auxiliary space: O(N)

Constraints:
1 ≤ Number of nodes ≤ 10⁵
1 ≤ Data of a node ≤ 10⁵