The one that comes to mind is how big your hash maps have to get before all the clever algorithms beat linear scan, and it's surprisingly large on modern computers: linear memory access is _very_ predictable.

The Roc and Zig folks probably have actual numbers.

Not sure if this counts, but I learned Huffman coding the intuitive tree-based way. From memory it was O(nlogn), but you can just O(n) it in-place in an array.

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