queues

JavaScript Queues

This section covers queue data structure implementations and problems in JavaScript, organized by difficulty level. All implementations use modern ES6+ JavaScript features and idioms.

Difficulty Levels

Basic

Fundamental queue concepts and implementations:

1. Implement Queue using Array
2. Design Circular Deque
3. Time Needed to Buy Tickets

Moderate

Intermediate queue problems from LeetCode:

1. Design Circular Queue
2. Implement Queue using Stacks
3. Sliding Window Maximum

Advanced

Challenging queue problems from LeetCode:

1. Number of Visible People in a Queue
2. Shortest Subarray with Sum at Least K
3. Find the Most Competitive Subsequence

Implementation Approach

Each problem is solved using multiple approaches showcasing different JavaScript features and patterns:

• Approach 1-2: Basic and optimized traditional implementations
• Approach 3: Implementation using modern JavaScript data structures (Map, Set)
• Approach 4: Functional programming approaches
• Approach 5: Advanced patterns (closures, higher-order functions)
• Approach 6: Generator functions for step-by-step visualization

Key JavaScript Features Used

• ES6+ syntax (arrow functions, destructuring, spread operator)
• Modern data structures (Map, Set)
• Functional programming patterns
• Factory functions
• Custom iterators with Symbol.iterator
• Generator functions for step-by-step visualization
• Performance testing utilities
• Comprehensive documentation with time/space complexity analysis

Usage

Navigate to any difficulty level directory and run the implementation files:

# Basic level
cd basic
node answer1.js

# Moderate level
cd moderate
node answer1.js

# Advanced level
cd advanced
node answer1.js

Performance Comparison

All implementations include performance testing utilities to compare different approaches:

// Performance comparison utility
const performanceTest = (QueueClass, name, operations) => {
  const start = performance.now();
  const queue = new QueueClass();
  
  // Enqueue operations
  for (let i = 0; i < operations; i++) {
    queue.push(i);
  }
  
  // Dequeue operations
  for (let i = 0; i < operations; i++) {
    queue.pop();
  }
  
  const end = performance.now();
  console.log(`${name}: ${end - start}ms for ${operations} operations`);
};

Source

Problems from GeeksforGeeks (Basic) and LeetCode (Moderate/Advanced):

• https://www.geeksforgeeks.org/queue-data-structure/
• https://leetcode.com/problemset/all/?topicSlugs=queue