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Grokking the Coding Interview Patterns in JavaScript

Connect All Siblings of a Binary Tree

Understand how to efficiently connect all nodes in a perfect binary tree from left to right using breadth-first search. This lesson helps you implement the next pointer to link each node to its immediate right sibling, handling the edge cases at each level and the last node. You will develop an O(n) time and O(1) space solution and practice coding this pattern to strengthen your tree traversal skills.

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Statement

Given the root of a perfect binary treeA binary tree in which all the levels are completely filled with nodes, and all leaf nodes (nodes with no children) are at the same level., where each node is equipped with an additional pointer, next, connect all nodes from left to right. Do so in such a way that the next pointer of each node points to its immediate right sibling except for the rightmost node, which points to the first node of the next level.

The next pointer of the last node of the binary tree (i.e., the rightmost node of the last level) should be set to NULL.

Constraints:

  • The number of nodes in the tree is in the range [0,500][0, 500].

  • −1000≤-1000 \leq Node.data ≤1000\leq 1000

Examples

canvasAnimation-image
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Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Connect All Siblings of a Binary Tree

1.

Which node will the next pointer of node 55 be pointing toward after connecting all the siblings in the given tree?

         _______ 1 _______
        |                  |
     __ 2 _             __ 3__
    |       |          |       |
   _4_    _ 5 _      - 6 -    --7--
  |   |  |     |    |     |  |     |
  8   9  10    11  12    13  14    15
A.

6

B.

4

C.

11

D.

5

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Note: As an additional challenge, we have intentionally hidden the solution to this puzzle.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4
5

Try it yourself

Implement your solution in connect_all_siblings.js in the following coding playground. You’ll need the provided supporting code to implement your solution.

We have left the solution to this challenge as an exercise for you. The optimal solution to this problem runs in O(n) time and takes O(1) space. You may try to translate the logic of the solved puzzle into a coded solution.

JavaScript
usercode > connect_all_siblings.js
import { EduTreeNode } from "./EduTreeNode.js";
function connectAllSiblings(root) {
    // Replace this placeholder return statement with your code
    
    return root
}
export {connectAllSiblings};
Connect All Siblings of a Binary Tree