Content warning: Advent of Code Day 11
Day 11 of #AdventOfCode is a classical graph problem like we're used to from previous years.
Unlike previously, I immediately thought of checking what the graph looked like with a visualization tool. Luckily, `petgraph` allows to export a graphviz file which can be then used to visualize the nodes and edges.
From that, it was clear that a few nodes were acting as "bridges" between largers subnets of nodes with no particular arrangement besides being directed towards the next "bridge" layer. Those bridge layers comprised 4 to 5 nodes in my input, and were the only ones with more than 6 incoming edges, so I used that as my filter criterion.
To gather them, I sorted the graph in topological order and chunked them by their position offset compared to the previous node. When doing this, all the nodes from a bridge layer end up being at most 20 positions away from the previous node in the sorted list.
Finally, I progressed through each subnet, collecting information about how many paths lead to each one of the end layer's nodes. By multiplying with all the paths leading to each start layer's node, we get the overall total number of paths.
#AoC #AoC2025 #AdventOfCode2025 #RustLang #rust
@JSkier@social.linux.pizza
