AlgoRung

DSA, one rung at a time 🪜 Patterns, animated LeetCode walkthroughs in Java, and System Design basics. New Short daily. Practise free at

[AlgoRung @algorung]

Find the smallest value in a rotated sorted array. Scanning it all is slow. One comparison tells you which half to drop.

Full Find Minimum in Rotated Sorted Array walkthrough: https://t.co/OTFi8n7QWR

#DSA #BinarySearch

[AlgoRung @algorung]

Checkout is slow. You have thirty services. Which one is it? Here's how you find out in ten seconds.

Full episode (System Design #37): https://t.co/sDz9M1cmZP

#SystemDesign #Observability

[AlgoRung @algorung]

Remove the third node from the end of a list, in one pass. No counting first.

Full Remove Nth Node From End of List walkthrough: https://t.co/eZKaSoY4JH

#DSA #LinkedList

[AlgoRung @algorung]

Ten million daily users. How many requests per second is that? Do it in your head in thirty seconds.

Full episode (System Design #36): https://t.co/cJv7oRCrzd

#SystemDesign #CapacityPlanning

[AlgoRung @algorung]

Give an order to take every course, so each prerequisite comes first. One queue does it.

Full Course Schedule II walkthrough: https://t.co/4hAO5D7G8C

#DSA #Graphs

[AlgoRung @algorung]

Ninety-nine percent uptime sounds amazing. It's three and a half days of downtime a year.

Full episode (System Design #35): https://t.co/t4Qn4I5gSn

#SystemDesign #HighAvailability

[AlgoRung @algorung]

How many ways can coins make an amount? The obvious recurrence gives the wrong count.

Full Coin Change II walkthrough: https://t.co/jV8AvaEFrp

#DSA #DynamicProgramming

[AlgoRung @algorung]

A network glitch, and suddenly two servers both think they're the leader. Here's how real systems make that impossible.

Full episode (System Design #34): https://t.co/wLL8atUqw2

#SystemDesign #Raft

[AlgoRung @algorung]

Is this a valid binary search tree? Checking each node against its parent is not enough.

Full Validate Binary Search Tree walkthrough: https://t.co/xT5Nc40ynx

#DSA #TreesBST

[AlgoRung @algorung]

The stock got reserved, the payment failed, and the item is stuck forever. Here's how real systems undo it.

Full episode (System Design #33): https://t.co/oDII45TcX3

#SystemDesign #SagaPattern

[AlgoRung @algorung]

Edit distance in one table: matching last letters are free (copy the diagonal), a mismatch costs 1 + the cheapest of replace, delete, insert.

Full walkthrough (LeetCode #72): https://t.co/e6tDxC2rir

#DSA #DynamicProgramming

[AlgoRung @algorung]

The newest edit was silently lost: a fast clock made an old write look newer. Order with logical clocks, not wall clocks.

Full episode (System Design #32): https://t.co/krkt60pVgB

#SystemDesign #DistributedSystems

[AlgoRung @algorung]

Network Delay Time: BFS gives the wrong answer with weighted links. Dijkstra with a min-heap finds every node's fastest time; the answer is the largest.

Full walkthrough (LeetCode #743): https://t.co/R8EN2OZnZ0

#DSA #Graphs

[AlgoRung @algorung]

Your lock expired while your server was frozen. It woke up and wrote anyway. Fix: fencing tokens, so storage rejects the stale holder.

Full episode (System Design #31): https://t.co/TQaAaGbIVL

#SystemDesign #DistributedSystems

[AlgoRung @algorung]

Shortest window of s that contains every letter of t: grow the right edge until it's valid, shrink the left while it stays valid. O(n).

Full walkthrough (LeetCode #76): https://t.co/YQfmQlPb7Y

#DSA #SlidingWindow

[AlgoRung @algorung]

One bot, 10,000 requests a second. A token bucket stops it: 10 tokens, refill 1 per second, each request takes one. Over the limit: 429.

Full episode (System Design #30): https://t.co/TNAZYoxIfB

#SystemDesign #RateLimiting

[AlgoRung @algorung]

Prefix search without scanning every word: a trie stores each shared prefix once. Insert, search, startsWith in O(word length).

Full walkthrough (LeetCode #208): https://t.co/uipMsplXtt

#DSA #Trie

[AlgoRung @algorung]

Tapped Pay once, charged twice? The response got lost and the app retried. Idempotency keys: same key on retry, server returns the saved result.

Full episode (System Design #29): https://t.co/o83wzfqkRT

#SystemDesign #APIDesign

[AlgoRung @algorung]

Every ordering of 1, 2, 3 with one template: choose an unused number, recurse, undo. The heart of backtracking.

Full walkthrough (LeetCode #46): https://t.co/STaBAqFkYm

#DSA #Backtracking

[AlgoRung @algorung]

Your checkout waits for an email? Publish one event to a queue and return. Consumers catch up. Expect duplicates: make them idempotent.

Full episode (System Design #28): https://t.co/s5LGuW2drn

#SystemDesign #Kafka