📌 Introduction

When I was in college, I practiced Data Structures and Algorithms (DSA) for placements, especially tree traversal techniques. I never thought I’d use them outside interviews… until I built an application in PHP (CodeIgniter) that had a multi-level user hierarchy, just like an n-ary tree.

This article is about how I used level-order traversal (aka BFS) to solve a real problem in production.

🏗️ The Problem: Multi-Level User Hierarchy

I had to build a system where users could have direct sub-users (referrals), and those users could have their own sub-users, and so on.

The structure looked like a tree:

User A
├── User B
│   ├── User D
│   └── User E
└── User C
    └── User F

We needed to show users a breakdown of their network:

• All users at level 1
• All users at level 2
• All users at level 3, etc.

🧩 The Solution: Level-Order Traversal

I recalled from my DSA days that level-order traversal (Breadth First Search) is perfect for this.

The idea is simple:

1. Start with the root user.
2. Use a queue to keep track of the next users to explore.
3. For each user, enqueue their direct children.
4. Keep track of the level of each user as you go.

💻 Sample Code (PHP + Eloquent)

Here’s a simplified version in Laravel-style PHP:

<?php

use SplQueue;

function getUsersByLevel(User $root, int $targetLevel)
{
    $queue = new SplQueue();
    
    $queue->enqueue([$root, 0]);
    
    $usersAtLevel = [];
    
    while (!$queue->isEmpty()) {
    
        [$user, $level] = $queue->dequeue();
        
        if ($level === $targetLevel) {
            $usersAtLevel[] = $user;
        }
        
        if ($level < $targetLevel) {
            foreach ($user->children as $child) {
                $queue->enqueue([$child, $level + 1]);
            }
        }
        
    }
    
    return $usersAtLevel;
}

🚀 Why This Was Cool

• I was applying textbook DSA in a live project.
• The performance was solid, no recursion hell or deep nesting.
• It made the logic readable, testable, and scalable.

🎯 Takeaway

DSA is not just for interviews.
If you understand the right tools and structures, you can write elegant solutions even in practical applications!