1745 posts · page 2 of 37
Solve Exclusive Time of Functions with a stack simulating a call stack. Python solution with timestamps, detailed trace, and edge case handling.
Implement a queue using two stacks with amortized O(1) operations. Covers costly enqueue vs costly dequeue approaches with Python code.
Design a Flatten Nested List Iterator using a stack for lazy flattening. Python solution with iterator protocol, step-by-step trace, and design analysis.
Find the largest rectangle in a histogram using a monotonic stack in O(n). Detailed walkthrough, Python code, visual trace, and common pitfalls.
Solve LeetCode 1249 Minimum Remove to Make Valid Parentheses using a stack. Two-pass and one-pass approaches with Python code and traces.
Find the maximal rectangle containing only 1s in a binary matrix. Builds on the largest rectangle in histogram technique with detailed explanation.
Maximum Frequency Stack solved with HashMap and stack groups by frequency. Python implementation with step-by-step trace, complexity analysis, and design insights.
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.
Design an Online Stock Span class (LeetCode 901) using a stack. Covers amortized analysis, Python implementation, and the price-span pair technique.
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.
Comprehensive catalog of 15+ stack and queue interview patterns with when-to-use guide, Python templates, complexity analysis, and problem mapping for coding interviews.
Solve LeetCode 316 Remove Duplicate Letters using monotonic stack with frequency and visited tracking. Smallest lexicographic subsequence in Python.
Learn to detect redundant parentheses in expressions using a stack. Covers the algorithm, Python implementation, and edge cases with traces.
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.
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.
Solve Simplify Path LeetCode 71 with a stack. Handle ., .., multiple slashes, and edge cases. Python solution with step-by-step trace.
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.
Learn how to sort a stack using only one additional stack. Step-by-step trace, Python implementation, and O(n²) complexity analysis.
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.
Solve the stock span problem efficiently using a monotonic stack. Includes brute force vs optimal approach, Python code, and visual trace.
Solve Sum of Subarray Minimums using the contribution technique with monotonic stacks. Python solution with modular arithmetic, traces, and O(n) analysis.
Solve Trapping Rain Water (LeetCode 42) using a stack-based approach. Python code with detailed trace, comparison with two-pointer, and complexity analysis.
Validate Stack Sequences solved by simulating push and pop operations. Python solution with step-by-step trace, edge cases, and complexity analysis for LeetCode 946.
Solve advanced binary search on answer problems — Koko eating bananas, ship packages, split array largest sum, minimize max distance to gas station, and magnetic force between balls.
Learn how to flatten a binary tree to a linked list using preorder threading, Morris traversal, and how to convert a BST to a sorted doubly linked list — with full Python implementations and Big-O analysis.
Master BST iterator using stack-based controlled in-order traversal, range sum queries, counting nodes in range, closest value, and closest K values — with full Python implementations.
Master every knapsack variant — 0/1 knapsack, unbounded knapsack, fractional knapsack, subset sum, partition equal subset, and target sum with Python solutions and Big-O analysis.
Master longest subsequence problems — LIS with patience sorting, longest bitonic, chain of pairs, zigzag subsequence, Russian doll envelopes (2D LIS).
Master DP on grids — unique paths, minimum path sum, dungeon game, cherry pickup, and maximum path in grid with step-by-step Python solutions.
Master palindrome DP problems — longest palindromic subsequence, minimum cuts for palindrome partitioning, counting palindromic substrings, and shortest palindrome with KMP.
Complete guide to all stock trading problems — I through IV, with cooldown, and with transaction fee. One unified state machine DP framework covers them all.
The complete DSA interview checklist — 75 essential problems organized by pattern, study schedules for 4, 8, and 12 weeks, a pattern recognition framework, and what interviewers actually look for.
Master space optimization — rolling arrays for DP, in-place algorithms, bit manipulation as sets, Morris traversal, constant-space linked list operations, and Floyd's cycle detection.
Derive character ordering from sorted alien words using topological sort, with course schedule variants and prerequisite chain problems.
Learn how to check if a graph is bipartite using BFS 2-coloring and DFS, with applications in matching, scheduling, and conflict detection.
Learn to clone graphs with BFS and DFS, validate graph trees, find minimum height trees via centroid decomposition, and reconstruct itineraries with Hierholzer's algorithm.
Master finding connected components using DFS, BFS, and Union-Find with applications to counting islands and grid connectivity problems.
Learn how to detect negative cycles using Bellman-Ford's nth relaxation, SPFA algorithm, and apply it to arbitrage detection in currency exchange graphs.
Master flood fill, surrounded regions, number of enclaves, and Pacific Atlantic water flow using DFS and BFS grid traversal techniques in Python.
Master the top 20 graph interview patterns with a BFS vs DFS decision flowchart, Union-Find strategies, grid vs adjacency list trade-offs, and template code.
Explore MST applications in network design, clustering, and competitive programming with second-best MST, critical edges, and minimum cost to connect points.
Master shortest path algorithms on grids including BFS for unweighted grids, 0-1 BFS with deque, and Dijkstra for weighted terrain with obstacles and portals.
Solve word search with DFS backtracking, Boggle with Trie pruning, and word ladder with BFS for efficient string transformation problems.
Learn to add two numbers represented as linked lists — both reverse order (LeetCode 2) and forward order (LeetCode 445). Covers carry handling, different-length lists, and Python implementations with Big-O analysis.
Learn two approaches to deep copy a linked list with random pointers — HashMap O(n) space and the interleaving O(1) space technique. Step-by-step walkthroughs with Python code and Big-O analysis.
Learn to flatten a multilevel doubly linked list (LeetCode 430) and flatten sorted linked lists. Covers iterative and recursive DFS approaches with Python implementations and Big-O analysis.
Master the top 15 linked list interview patterns — dummy node, fast-slow pointers, reversal, merge, partition, and more. Includes common mistakes, a time complexity cheatsheet, and a decision flowchart.
Learn three ways to check if a linked list is a palindrome — stack-based O(n) space, reverse-second-half O(1) space, and recursive. Step-by-step walkthroughs with Python code and Big-O analysis.