The same would be true for the initial map: Replacing encountered := map[uint64]bool{} with encountered := make(map[uint64]bool, len(elements)) Should

The same would be true for the initial map: Replacing encountered := map[uint64]bool{} with encountered := make(map[uint64]bool, len(elements)) Should be faster. Golang Hashmaps initially have one bucket with a size of 8. If more elements are added new buckets are created. So giving a hint to initialize a correct number of things should always be faster.