ocaml: phase 5.1 min_meeting_rooms.ml baseline (8 meetings, min 4 rooms)

Sweep-line algorithm via separately-sorted starts / ends arrays:

  while i < n do
    if starts[i] < ends[j] then begin busy++; rooms = max; i++ end
    else begin busy--; j++ end
  done

  intervals: (0,30) (5,10) (15,20) (10,25) (5,12)
             (20,35) (0,5)  (8,18)

At time 8, meetings (0,30), (5,10), (5,12), (8,18) are all active
simultaneously -> answer = 4.

Tests local helper bound via let (`let bubble a = ...`) for
in-place sort, dual-pointer sweep on parallel ordered event streams.

193 baseline programs total.

plans/ocaml-on-sx.md

@@ -407,6 +407,15 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-11 Phase 5.1 — min_meeting_rooms.ml baseline (sweep-line
+  for min concurrent meetings on 8 intervals = 4). Separate starts
+  and ends arrays sorted independently, then a two-pointer sweep:
+  on start<end push a new room (busy+1), else release one (busy-1).
+  Intervals: (0,30) (5,10) (15,20) (10,25) (5,12) (20,35) (0,5)
+  (8,18). At time 8: meetings (0,30), (5,10), (5,12), (8,18) all
+  active → 4 simultaneous = answer. Tests local recursive helper
+  `let bubble a = …` for in-place sort, dual-pointer sweep on
+  ordered events. 193 baseline programs total.
 - 2026-05-11 Phase 5.1 — activity_select.ml baseline (greedy
   earliest-end-time activity selection on 11 intervals → max
   non-overlapping 4). Sort intervals by end time (bubble sort to