test.ml

open Base

let max_population intervals =
  let t = Hashtbl.create (module Int) in
  List.iter intervals (fun (birth, dead) ->
      Hashtbl.update t birth (function | None -> 1 | Some i -> i + 1);
      Hashtbl.update t dead (function | None -> -1 | Some i -> i - 1));
  let years = List.sort ~compare:Int.compare (Hashtbl.keys t) in
  let max = ref 0 in
  let current = ref 0 in
  List.iter years (fun y ->
      current := !current + Hashtbl.find_exn t y;
      if !current > !max then max := !current);
  !max