Queues: 50 Leetcode Questions

#leetcode #queue

Easy Questions (20 Questions)

Implement Queue using Stacks (232)

Implement a queue using two stacks to handle enqueue and dequeue operations.
Design Circular Queue (622)

Design a circular queue supporting efficient operations with a fixed capacity.
Moving Average from Data Stream (346)

Maintain a moving average of integers from a data stream using a fixed-size queue.
Number of Recent Calls (933)

Count the number of calls received within a given time frame using a sliding window.
First Unique Character in a String (387)

Find the first non-repeating character in a string using a queue.
Perfect Squares (279)

Find the least number of perfect square numbers that sum up to a given number using BFS.
Open the Lock (752)

Find the minimum steps to unlock a combination lock using BFS.
Rotting Oranges (994)

Determine the minimum time to rot all oranges in a grid using multi-source BFS.
Binary Tree Level Order Traversal (102)

Perform a level-order traversal of a binary tree using a queue.
Symmetric Tree (101)

Check if a binary tree is symmetric using BFS with a queue.
Shortest Path in Binary Matrix (1091)

Find the shortest path from the top-left to the bottom-right in a binary grid.
Walls and Gates (286)

Fill each empty room with the distance to its nearest gate using multi-source BFS.
Island Perimeter (463)

Calculate the perimeter of an island represented in a grid.
Breadth-First Search Traversal

Implement BFS traversal for a graph using a queue.
Time Needed to Inform All Employees (1376)

Find the time required to inform all employees in a hierarchy using BFS.
Course Schedule (207)

Check if all courses can be finished given prerequisites using topological sorting.
Flood Fill (733)

Perform a flood-fill operation on a grid using BFS.
Snakes and Ladders (909)

Find the minimum moves to reach the last square in a snakes and ladders game.
Binary Tree Zigzag Level Order Traversal (103)

Traverse a binary tree in a zigzag level order using a queue.
Sliding Window Maximum (239)

Find the maximum value in each sliding window of size k.

Medium Questions (25 Questions)

Design Front Middle Back Queue (1670)

Implement a double-ended queue with front, middle, and back operations.
Top K Frequent Elements (347)

Find the top k most frequent elements in an array using a priority queue.
Find the Winner of the Circular Game (1823)

Simulate a circular game using a queue to determine the winner.
Jump Game VI (1696)

Find the maximum score you can achieve in a jump game with a sliding window queue.
Course Schedule II (210)

Find the order of courses to finish all given prerequisites using BFS.
K Closest Points to Origin (973)

Find the k closest points to the origin using a priority queue.
Task Scheduler (621)

Schedule tasks with cooling intervals using a queue.
Reorganize String (767)

Rearrange a string so that no two adjacent characters are the same using a priority queue.
Sum of Subarray Minimums (907)

Calculate the sum of minimum values of all subarrays using monotonic queues.
Cheapest Flights Within K Stops (787)

Find the cheapest flight route with at most k stops using a queue for BFS.
Reach a Number (754)

Find the minimum steps to reach a target number starting from zero.
Count Complete Tree Nodes (222)

Count the number of nodes in a complete binary tree using BFS.
Shortest Bridge (934)

Find the shortest bridge between two islands using BFS.
Remove All Adjacent Duplicates in String II (1209)

Remove adjacent duplicates in a string with a stack-queue hybrid approach.
Kth Largest Element in a Stream (703)

Find the kth largest element from a dynamic data stream.
Escape the Spreading Fire (2428)

Determine the earliest escape time given fire spreading on a grid.
Data Stream as Disjoint Intervals (352)

Add intervals from a stream and return a disjoint set of intervals.
Sliding Puzzle (773)

Solve a sliding puzzle using BFS to reach the goal state.
Maximum Performance of a Team (1383)

Select a team to maximize performance using a priority queue.
Sequential Digits (1291)

Generate numbers with sequential digits in a given range using BFS.
The Maze (490)

Determine if the ball can stop at the destination in a maze using BFS.
Find Eventual Safe States (802)

Find nodes in a graph that are eventually safe using BFS.
Kill Process (582)

Kill a process and its children given a parent-child relationship.
Employee Importance (690)

Calculate the total importance of an employee and their subordinates.
Design Hit Counter (362)

Count the number of hits in a given time frame using a sliding window queue.

Hard Questions (5 Questions)

Minimum Cost to Connect Sticks (1167)

Connect sticks of varying lengths with the minimum cost using a priority queue.
Merge k Sorted Lists (23)

Merge k sorted linked lists into one sorted list using a priority queue.
LFU Cache (460)

Design an LFU (Least Frequently Used) cache with efficient operations.
Minimum Number of Refueling Stops (871)

Determine the minimum number of refueling stops to reach a target.
Swim in Rising Water (778)

Find the minimum time to swim from the top-left to the bottom-right in a grid.

By practicing these queue-related problems, you’ll develop a solid understanding of queue operations and their real-world applications. Which one are you solving first?