Somewhat exhasperated as I should be making more progress. Went through 4 prototypes the last 3 days to get to a final working solution. Now throwing out the bits that didn't work. Here's a fast adjaceny builder using nothing but arrays. No hash. No sorts. https://gist.github.com/dwilliamson/e6250dcb280cecc976d11ac12fc11a59

Just added a quick BFS example. If you can use this, great! Seems a shame to waste :)