Given a string text, return how often each character occurs, as entries like "l:3", listed in the order the characters first appear. Spaces are not counted, and upper- and lowercase letters count separately. This is frequency counting applied to characters. Rescanning the text for every new character works but costs O(n²); counting everything in one pass into a map is O(n). The extra requirement — report in first-appearance orderInsertion OrderThe order in which keys were first added to a map. Some maps remember it; others do not. — matters when choosing the map type.