Leetcode968

private static int CoverLogic(TreeNode node, Stack<TreeNode> stack, HashSet<TreeNode> covered, int minCamera)
{
    //if node has any uncovered child, then cover it and it's parent(if any) 
    if ((node.left != null && !covered.Contains(node.left)) || (node.right != null && !covered.Contains(node.right)))
    {
        minCamera++;
        covered.Add(node);

        if (stack.Any()) //has parent
        {
            //cover parent too
            covered.Add(stack.Peek());
        }
    }
    //if node is root and is not covered, then cover it
    else if (!stack.Any() && !covered.Contains(node))
    {
        minCamera++;
        covered.Add(node);
    }
    return minCamera;
}
     
public int MinCameraCover(TreeNode root) {
    int minCamera = 0;

    //Set contains, list of all coverted nodes
    HashSet<TreeNode> covered = new HashSet<TreeNode>();

    //Iterative - POST Order traversal
    Stack<TreeNode> stack = new Stack<TreeNode>();
    while (root != null || stack.Any())
    {
        while (root != null)
        {
            stack.Push(root);
            root = root.left;
        }

        TreeNode temp = stack.Peek();
        if (temp.right == null)
        {
            temp = stack.Pop();
            //Console.Write(temp.val + " ");

            minCamera = CoverLogic(temp, stack, covered, minCamera);

            //if the popped elemnt is the right of its parent
            while (stack.Any() && temp == stack.Peek().right)
            {
                temp = stack.Pop();
                //Console.Write(temp.val + " ");

                minCamera = CoverLogic(temp, stack, covered, minCamera);
            }
        }
        else
        {
            root = temp.right;
        }
    }
    return minCamera;
}