Uploads from Xah Lee

Currently Playing: Xah Ep732 Wolfram Language, Advent of Code 2025, Day 4, part 2. take 2

Video Summary (Generated by AI, Edited by Human.) This video discusses the solution to Advent of Code 2025, Day 4, Part 2 (0:12). The problem involves a grid of @ signs and dots, where the goal is to iteratively remove @ signs that have fewer than four @ neighbors until no more can be removed. The final answer is the total number of @ signs removed (3:40). The presenter, Xah Lee, codes the solution in Wolfram Language (Mathematica), emphasizing a pure functional programming approach with no variable mutation, for loops, or object-oriented concepts (39:50). He breaks down the problem into sub-functions: Identifying special @ signs: Finding @ signs with less than four @ neighbors (2:36). Removing @ signs: Replacing identified @ signs with zeros in the matrix (1:08:49). Iterative process: Repeating the removal until no more @ signs can be removed, using the FixedPoint function in Wolfram Language (13:18). The presenter demonstrates debugging steps when the initial code doesn't work, leading to the identification of an incorrect approach to "deleting" elements from the matrix (1:08:49). The final solution for the toy example yields 43 removed @ signs (1:14:41). Notes at http://xahlee.info/talk_show/xah_talk_show_ep732.html If browser says security error, that is because it auto changes URL from HTTP to HTTPS. It's a way to censor 22 million old websites. Remove the S in HTTPS. Or use brave browser or safari.