Queue Data Structure

Data Structure and Algorithms Course
Practice Problems on Queue
Recent articles on Queue

What is Queue Data Structure?

A Queue is defined as a linear data structure that is open at both ends and the operations are performed in First In First Out (FIFO) order.

We define a queue to be a list in which all additions to the list are made at one end, and all deletions from the list are made at the other end.  The element which is first pushed into the order, the operation is first performed on that.

Queue Data Structure

FIFO Principle of Queue:

• A Queue is like a line waiting to purchase tickets, where the first person in line is the first person served. (i.e. First come first serve).
• Position of the entry in a queue ready to be served, that is, the first entry that will be removed from the queue, is called the front of the queue(sometimes, head of the queue), similarly, the position of the last entry in the queue, that is, the one most recently added, is called the rear (or the tail) of the queue. See the below figure.

Fifo Property in Queue

Characteristics of Queue:

• Queue can handle multiple data.
• We can access both ends.
• They are fast and flexible. 

Queue Representation:

Like stacks, Queues can also be represented in an array: In this representation, the Queue is implemented using the array. Variables used in this case are

• Queue: the name of the array storing queue elements.
• Front: the index where the first element is stored in the array representing the queue.
• Rear: the index where the last element is stored in an array representing the queue.

Topics :

Introduction to Queue Data Structure:

1. Introduction to Queue – Data Structure and Algorithm Tutorials
2. Implementations of Queue Data Structure using Arrays
3. Implementations of Queue Data Structure using Linked List
4. Applications, Advantages and Disadvantages of Queue
5. Different Types of Queue

Implementation of Queue in various Programming Languages:

1. Queue in C++ Standard Template Library (STL)
2. Queue Interface In Java
3. Queue In Python
4. Queue In C#
5. Queue in Javascript
6. Queue in Go Language
7. Queue in Scala

Some other Implementations of Queue Data Structure:

1. Implementation of Deque using doubly linked list
2. Implement a stack using single queue
3. Implement Queue using Stacks
4. Implement Stack using Queues
5. How to efficiently implement k Queues in a single array?
6. LRU Cache Implementation

Some Must Solve Standard Problems on Queue Data Structure:

• Easy:
  1. Queue – Linked List Implementation
  2. Implement Stack using Queues
  3. Queue using Stacks
  4. Detect cycle in an undirected graph using BFS
  5. Breadth First Search or BFS for a Graph
  6. Traversing directory in Java using BFS
  7. Vertical order traversal of Binary Tree using Map
  8. Print Right View of a Binary Tree
  9. Find Minimum Depth of a Binary Tree
  10. Difference between BFS and DFS
  11. Check whether a given graph is Bipartite or not
  12. Find the Maximum Depth or Height of given Binary Tree
• Medium:
  1. Flatten a multilevel linked list
  2. Level with maximum number of nodes
  3. Find if there is a path between two vertices in a directed graph
  4. Queue using Stacks
  5. Implement Stack using Queues
  6. Print all nodes between two given levels in Binary Tree
  7. Minimum steps to reach target by a Knight
  8. Islands in a graph using BFS
  9. Deletion in a Binary Tree
  10. Level order traversal line by line | Set 3 (Using One Queue)
  11. Clockwise Spiral Traversal of Binary Tree
  12. Reverse Level Order Traversal
  13. Perfect Binary Tree Specific Level Order Traversal
  14. Print Left View of a Binary Tree
  15. Check whether a given Binary Tree is Complete or not
  16. Diagonal Traversal of Binary Tree
  17. Print leftmost and rightmost nodes of a Binary Tree
  18. Convert a Binary Tree into Doubly Linked List in spiral fashion
  19. Check if a given Binary Tree is a Heap
  20. Reverse alternate levels of a perfect binary tree
• Hard:
  1. Sliding Window Maximum (Maximum of all subarrays of size K)
  2. Flood Fill Algorithm
  3. Find shortest safe route in a path with landmines
  4. Shortest path in a Binary Maze
  5. An Interesting Method to Generate Binary Numbers from 1 to n
  6. Maximum cost path from source node to destination
  7. Convert BST to Min Heap
  8. Shortest distance between two cells in a matrix or grid
  9. Find next right node of a given key
  10. Snake and Ladder Problem
  11. Find shortest safe route in a path with landmines
  12. Maximum cost path from source node to destination
  13. Count all possible walks from a source to a destination …
  14. Minimum Cost of Simple Path between two nodes in a …
  15. Traversing directory in Java using BFS
  16. Minimum Cost Path in a directed graph via given set of …
  17. LRU Cache Implementation
  18. Find the first circular tour that visits all petrol pumps
  19. Find the first non-repeating character from a stream of characters
  20. Sliding Window Maximum (Maximum of all subarrays of size K)
  21. Minimum time required to rot all oranges

Quick Links:

• ‘Practice Problems’ on Queue
• ‘Videos’ on Queue
• ‘Quizzes’ on Queue

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