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Grokking the Coding Interview Patterns in JavaScript

Connect All Siblings of a Binary Tree

Explore how to connect each node to its adjacent sibling in a perfect binary tree using breadth-first search. Learn to assign next pointers across levels, enabling traversal from left to right, and solve this with O(n) time and constant space.

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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 each node to the next node from left to right. For nodes that have a right sibling, next points to that sibling. For the rightmost node of each level, next points to the first node of the next level. The rightmost node of the final level points 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