You are given a root of a binary tree that has n number of nodes. You have to return the right-side view in the form of a list. A right-side view of a binary tree is the data of the nodes that are visible when the tree is viewed from the right side.

binary-tree-right-side.js

import { TreeNode } from "./ds_v1/BinaryTree.js";
// Definition of a binary tree node
// class TreeNode {
//   constructor(data) {
//     this.data = data;
//     this.left = null;
//     this.right = null;
//   }
// }

function rightSideView(root) {
  const result = [];

  if (!root) {
    return result;
  }

  // stack for DFS
  // stack item = tuple [node, level]
  // start with root node at level 0
  const stack = [[root, 0]];
  while (stack.length > 0) {
    const [node, level] = stack.pop();
    if (result.length === level) {
      // if result length is equal to level
      // it means we need to add this node
      // for example length === 0, meaning we need to add node from level 0 (root node)
      result.push(node.data);
    }
    // push left first
    if (node.left) {
      stack.push([node.left, level + 1]);
    }
    // push right second, so when we pop, we pop right first, going DFS into the right subtree first
    if (node.right) {
      stack.push([node.right, level + 1]);
    }
    // after we went through the right subtree we will start walking through left subtree,
    // but since our result array is already filled with values, we won't be adding any values from levels we've visited
    // we will only add more values on levels that were not present in the initial right subtree
  }

  // Replace this placeholder return statement with your code
  return result;
}

export { rightSideView };

// tc: O(n)
// sc: O(h