DSA Solutions & Explanations

Each solution breaks the problem into approaches, usually from brute force to the best one, and explains why each works. Code comes in Python, Java, C++ and other languages. Knowing why an approach works matters more in an interview than remembering the code.

Try the problem first. Give it at least 20 minutes before you open the solution.
Read every approach. The brute force shows you the problem; the faster ones show the pattern.
Check the complexity. Note the time and space of each approach and what makes the difference.
Write it yourself. Close the solution and code it from memory in the editor.
Come back in a week. Solving it again later is what makes the pattern stick.

All problems Topics Company questions Sheets

Solutions, explained

269.Alien Dictionary

329.Longest Increasing Path in a Matrix

332.Reconstruct Itinerary

499.The Maze III

685.Redundant Connection II

753.Cracking the Safe

765.Couples Holding Hands

834.Sum of Distances in Tree

847.Shortest Path Visiting All Nodes

882.Reachable Nodes In Subdivided Graph

913.Cat and Mouse

924.Minimize Malware Spread

928.Minimize Malware Spread II

1168.Optimize Water Distribution in a Village

1192.Critical Connections in a Network

1203.Sort Items by Groups Respecting Dependencies

1298.Maximum Candies You Can Get from Boxes

1368.Minimum Cost to Make at Least One Valid Path in a Grid

1377.Frog Position After T Seconds

1489.Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree

1494.Parallel Courses II

1548.The Most Similar Path in a Graph

1579.Remove Max Number of Edges to Keep Graph Fully Traversable

1591.Strange Printer II

1632.Rank Transform of a Matrix

1697.Checking Existence of Edge Length Limited Paths

1719.Number Of Ways To Reconstruct A Tree

1724.Checking Existence of Edge Length Limited Paths II

1728.Cat and Mouse II

1761.Minimum Degree of a Connected Trio in a Graph

1782.Count Pairs Of Nodes

1857.Largest Color Value in a Directed Graph

1916.Count Ways to Build Rooms in an Ant Colony

1928.Minimum Cost to Reach Destination in Time

2045.Second Minimum Time to Reach Destination

2050.Parallel Courses III

2065.Maximum Path Quality of a Graph

2076.Process Restricted Friend Requests

2092.Find All People With Secret

2123.Minimum Operations to Remove Adjacent Ones in Matrix

2127.Maximum Employees to Be Invited to a Meeting

2203.Minimum Weighted Subgraph With the Required Paths

2204.Distance to a Cycle in Undirected Graph

2242.Maximum Score of a Node Sequence

2246.Longest Path With Different Adjacent Characters

2290.Minimum Obstacle Removal to Reach Corner

2307.Check for Contradictions in Equations

2328.Number of Increasing Paths in a Grid

2360.Longest Cycle in a Graph

2371.Minimize Maximum Value in a Grid

How to use these solutions