package main

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func rightSideView(root *TreeNode) (out []int) {
	if root == nil {
		return
	}
	for stack := []*TreeNode{root}; len(stack) != 0; {
		top := stack[len(stack)-1]
		if len(stack) > len(out) {
			out = append(out, top.Val)
		}
		if top.Right != nil {
			stack = append(stack, top.Right)
		} else if top.Left != nil {
			stack = append(stack, top.Left)
		} else {
			stack = stack[:len(stack)-1]
			if len(stack) != 0 {
				new_top := stack[len(stack)-1]
				// Easiest way to DFS by modification of tree.
				// There was no requirement to keep it intact ¯\_(ツ)_/¯.
				if new_top.Right == top {
					new_top.Right = nil
				} else {
					new_top.Left = nil
				}
			}
		}
	}
	return
}