Deque Design Patterns — Sliding Window, Palindrome, Work Stealing
Master deque design patterns including sliding window maximum, palindrome checking, work stealing, and BFS/DFS hybrid. Python implementations.
·7 min read · #dsa#queues#deque
#dsa
277 posts · page 1 of 6
Priority Queue Patterns — Top-K, Merge K Lists, Median, Dijkstra
Master priority queue patterns for coding interviews. Top-K elements, merge K sorted lists, running median, and Dijkstra's algorithm in Python.
·7 min read · #dsa#heaps#priority-queue
BFS Pattern with Queues: Level-Order and Shortest Path
Master BFS using queues for tree level-order traversal and shortest path in unweighted graphs. Python implementations with detailed traces.
·3 min read · #dsa#queues#intermediate
Design Circular Deque — Array-Based Implementation (LeetCode 641)
Design a Circular Deque with front/rear pointers on a fixed-size array. Python solution with all O(1) operations, visual trace, and edge case handling.
·6 min read · #dsa#queues#design
Design Front Middle Back Queue — Two Deques (LeetCode 1670)
Design Front Middle Back Queue using two balanced deques. Python solution with O(1) operations, step-by-step trace, and complexity analysis for LeetCode 1670.
·6 min read · #dsa#queues#design
Design Hit Counter Using Queue
Design a hit counter that counts hits in the past 5 minutes using a queue. LeetCode 362 solution with O(1) amortized operations.
·3 min read · #dsa#queues#intermediate
First Non-Repeating Character in a Stream
Find the first non-repeating character in a character stream using a queue and hash map. Python solution with O(1) amortized per query.
·3 min read · #dsa#queues#intermediate
Implement Stack Using Two Queues — Two Approaches Explained
Implement a stack using two queues with costly push and costly pop approaches. Complete Python solutions with complexity analysis.
·4 min read · #dsa#stacks#queues
Moving Average from Data Stream Using Queue
Calculate the moving average from a data stream using a queue with fixed window size. LeetCode 346 solution with O(1) per operation.
·2 min read · #dsa#queues#beginner
Jump Game III and IV — BFS with Queue
Solve Jump Game III (LeetCode 1306) and Jump Game IV (LeetCode 1345) using BFS. Covers graph modeling of array problems with queue-based traversal.
·4 min read · #dsa#queues#intermediate
Number of Recent Calls — Queue-Based Sliding Window (LeetCode 933)
Solve Number of Recent Calls using a queue as a 3000ms sliding window counter. Python solution with deque, step-by-step trace, and amortized analysis.
·6 min read · #dsa#queues#easy
Rotten Oranges — Multi-Source BFS with Queue
Solve the Rotten Oranges problem (LeetCode 994) using multi-source BFS. Covers the simultaneous spread pattern, Python code, and grid BFS template.
·4 min read · #dsa#queues#intermediate
Open the Lock — BFS on State Space (LeetCode 752)
Open the Lock problem solved with BFS on 4-digit state space. Python solution with deadend handling, bidirectional BFS optimization, and complexity analysis.
·6 min read · #dsa#queues#bfs
Shortest Path in Binary Matrix — BFS Solution
Find the shortest path in a binary matrix using BFS with 8-directional movement. LeetCode 1091 solution with Python code and grid traversal tips.
·3 min read · #dsa#queues#intermediate
Sliding Window Maximum Using Deque
Solve the sliding window maximum problem in O(n) using a monotonic deque. Covers the algorithm, Python code, visual traces, and variations.
·4 min read · #dsa#queues#advanced
Shortest Subarray with Sum at Least K — Monotonic Deque (LeetCode 862)
Shortest Subarray with Sum at Least K solved with monotonic deque and prefix sums. Python solution with detailed trace, complexity analysis, and edge cases.
·7 min read · #dsa#queues#deque
Task Scheduler — Queue + Heap Approach
Solve the Task Scheduler problem (LeetCode 621) using a queue and max-heap. Covers the greedy formula and simulation approaches with Python code.
·3 min read · #dsa#queues#advanced
Walls and Gates — Multi-Source BFS
Fill each empty room with the distance to its nearest gate using multi-source BFS. LeetCode 286 solution with Python code and grid BFS template.
·3 min read · #dsa#queues#intermediate
Snakes and Ladders BFS — Shortest Path on Game Board (LeetCode 909)
Solve Snakes and Ladders with BFS to find minimum dice rolls. Python solution with 1D-2D conversion, boustrophedon layout, and step-by-step trace.
·7 min read · #dsa#queues#bfs
Zigzag Level Order Traversal — BFS with Deque in Python
Zigzag level order traversal of a binary tree using BFS and deque. Step-by-step Python solution with visual trace, complexity analysis, and interview tips.
·5 min read · #dsa#queues#trees
Word Ladder BFS Approach — Shortest Transformation Sequence
Word Ladder solved with BFS and pattern matching optimization. Step-by-step Python solution for LeetCode 127 with complexity analysis and interview tips.
·6 min read · #dsa#queues#bfs
132 Pattern — Monotonic Stack with Reverse Traversal (LeetCode 456)
Solve the 132 Pattern problem using a monotonic stack scanning right to left. Python solution tracking s3 candidates and s2 maximum, with detailed trace.
·7 min read · #dsa#stacks#advanced
Asteroid Collision Problem Using Stacks
Solve the asteroid collision problem (LeetCode 735) using a stack. Covers collision rules, Python implementation, and all edge cases.
·3 min read · #dsa#stacks#intermediate
Basic Calculator I, II, III — Complete Expression Evaluation Guide
Solve Basic Calculator problems LeetCode 224, 227, and 772. Master stack-based expression evaluation with +, -, *, /, and parentheses in Python.
·6 min read · #dsa#stacks#advanced
Car Fleet Problem — Stack-Based Arrival Time Solution
Solve LeetCode 853 Car Fleet using a stack. Sort by position, compare arrival times, and count fleets. Python solution with visual trace.
·5 min read · #dsa#stacks#sorting
The Celebrity Problem Using Stack-Based Elimination
Solve the celebrity problem in O(n) time using a stack elimination technique. Includes proof of correctness, Python code, and matrix examples.
·4 min read · #dsa#stacks#intermediate
Decode String (LeetCode 394) — Nested Bracket Decoding
Decode nested encoded strings like '3[a2[c]]' using a stack. Complete walkthrough with Python solution, traces, and edge cases.
·3 min read · #dsa#stacks#intermediate
Evaluate Reverse Polish Notation — Stack Solution Explained
Solve LeetCode 150 Evaluate Reverse Polish Notation using a stack. Python implementation with division gotcha, traces, and complexity analysis.
·5 min read · #dsa#stacks#intermediate
Exclusive Time of Functions — Call Stack Simulation (LeetCode 636)
Solve Exclusive Time of Functions with a stack simulating a call stack. Python solution with timestamps, detailed trace, and edge case handling.
·6 min read · #dsa#stacks#intermediate
Implement Queue Using Two Stacks — Amortized O(1) Solution
Implement a queue using two stacks with amortized O(1) operations. Covers costly enqueue vs costly dequeue approaches with Python code.
·5 min read · #dsa#stacks#queues
Flatten Nested List Iterator — Lazy Stack Design (LeetCode 341)
Design a Flatten Nested List Iterator using a stack for lazy flattening. Python solution with iterator protocol, step-by-step trace, and design analysis.
·6 min read · #dsa#stacks#design
Largest Rectangle in Histogram Using Stack
Find the largest rectangle in a histogram using a monotonic stack in O(n). Detailed walkthrough, Python code, visual trace, and common pitfalls.
·4 min read · #dsa#stacks#advanced
Minimum Remove to Make Valid Parentheses — Stack Solution
Solve LeetCode 1249 Minimum Remove to Make Valid Parentheses using a stack. Two-pass and one-pass approaches with Python code and traces.
·5 min read · #dsa#stacks#strings
Maximal Rectangle in Binary Matrix
Find the maximal rectangle containing only 1s in a binary matrix. Builds on the largest rectangle in histogram technique with detailed explanation.
·3 min read · #dsa#stacks#advanced
Maximum Frequency Stack — HashMap + Stack Groups (LeetCode 895)
Maximum Frequency Stack solved with HashMap and stack groups by frequency. Python implementation with step-by-step trace, complexity analysis, and design insights.
·6 min read · #dsa#stacks#design
Next Greater Element II — Circular Array with Monotonic Stack (LeetCode 503)
Next Greater Element II solved with monotonic stack and circular array double-length trick. Python solution with step-by-step trace, complexity analysis, and patterns.
·7 min read · #dsa#stacks#monotonic-stack
Online Stock Span — Class Design with Stack
Design an Online Stock Span class (LeetCode 901) using a stack. Covers amortized analysis, Python implementation, and the price-span pair technique.
·3 min read · #dsa#stacks#intermediate
Next Smaller Element Using Stack — Monotonic Increasing Stack Pattern
Solve the Next Smaller Element problem with a monotonic increasing stack in O(n). Python code, step-by-step trace, and reusable pattern for interviews.
·6 min read · #dsa#stacks#intermediate
Stack and Queue Interview Patterns — 15+ Patterns Catalog
Comprehensive catalog of 15+ stack and queue interview patterns with when-to-use guide, Python templates, complexity analysis, and problem mapping for coding interviews.
·9 min read · #dsa#stacks#queues
Remove Duplicate Letters — Monotonic Stack + Greedy Solution
Solve LeetCode 316 Remove Duplicate Letters using monotonic stack with frequency and visited tracking. Smallest lexicographic subsequence in Python.
·5 min read · #dsa#stacks#greedy
Detect Redundant Parentheses Using a Stack
Learn to detect redundant parentheses in expressions using a stack. Covers the algorithm, Python implementation, and edge cases with traces.
·3 min read · #dsa#stacks#intermediate
Real-World Applications of Stacks and Queues — From Undo/Redo to BFS Crawlers
Real-world applications of stacks and queues: undo/redo systems, browser history, call stacks, task scheduling, message queues, and BFS web crawlers with Python examples.
·7 min read · #dsa#stacks#queues
Remove K Digits to Make Smallest Number
Use a monotonic stack to remove k digits from a number to make it as small as possible. LeetCode 402 solution with Python code and traces.
·4 min read · #dsa#stacks#intermediate
Simplify Unix Path Using a Stack — LeetCode 71 Solution
Solve Simplify Path LeetCode 71 with a stack. Handle ., .., multiple slashes, and edge cases. Python solution with step-by-step trace.
·4 min read · #dsa#stacks#strings
Score of Parentheses — Stack-Based Scoring (LeetCode 856)
Solve Score of Parentheses using a stack to track nested scores. Python solution with trace, O(n) time, plus the bit-shift trick for O(1) space.
·6 min read · #dsa#stacks#intermediate
Sort a Stack Using Another Stack
Learn how to sort a stack using only one additional stack. Step-by-step trace, Python implementation, and O(n²) complexity analysis.
·3 min read · #dsa#stacks#intermediate
Tag Validator — Stack-Based XML Parsing (LeetCode 591)
Tag Validator solved with stack-based HTML/XML tag matching and CDATA parsing. Python solution with edge cases, step-by-step trace, and complexity analysis.
·6 min read · #dsa#stacks#strings
Stock Span Problem Using Stacks
Solve the stock span problem efficiently using a monotonic stack. Includes brute force vs optimal approach, Python code, and visual trace.
·4 min read · #dsa#stacks#intermediate