https://www.rik-kisnah.ai/tags/graphs/Recent content in Graphs on Rik Kisnah - BlogHugoenTue, 20 Jan 2026 09:00:00 -0800https://www.rik-kisnah.ai/teach/coding/connected-components-union-find/Tue, 20 Jan 2026 09:00:00 -0800https://www.rik-kisnah.ai/teach/coding/connected-components-union-find/Given a list of friendships, how many separate friend groups are there? Everyone starts as their own group. Each friendship merges two groups. A tiny structure with two operations answers it almost instantly, and it is what real systems use to track which servers are in which cluster.https://www.rik-kisnah.ai/teach/systems/design-a-web-crawler/Tue, 16 Aug 2022 09:00:00 -0700https://www.rik-kisnah.ai/teach/systems/design-a-web-crawler/Start with a few pages, follow every link, and visit the whole web without visiting anything twice or knocking any site over. A giant breadth-first search with a to-do list on disk, a seen-set that fits in memory, and a rule to be nice.https://www.rik-kisnah.ai/teach/coding/clone-graph/Tue, 13 Oct 2020 09:00:00 -0700https://www.rik-kisnah.ai/teach/coding/clone-graph/Make an exact copy of a graph where nodes point at each other, possibly in loops. The only new idea over a tree is a map from old node to new node, so you never copy anyone twice and never get stuck going round in circles.https://www.rik-kisnah.ai/teach/coding/flood-fill/Tue, 03 Dec 2019 09:00:00 -0800https://www.rik-kisnah.ai/teach/coding/flood-fill/The paint bucket tool. Click a square, and every connected square of the same colour changes too. Spread to the four neighbours, stop at a different colour or the edge. It is the same search you will use on every grid problem after this one.