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(* Day 2: Part 1 *)
type level = int
type reports = level list list
let rec compare_report_levels_helper comparison prev report =
match report with
| [] -> true
| h :: t -> comparison prev h && compare_report_levels_helper comparison h t
let compare_report_levels comparison report =
match report with
| [] -> true
| h :: t -> compare_report_levels_helper comparison h t
let all_increasing report = compare_report_levels ( < ) report
let all_decreasing report = compare_report_levels ( > ) report
let at_least_one report =
compare_report_levels (fun prev curr -> prev <> curr) report
let at_most_three report =
compare_report_levels (fun prev curr -> abs (prev - curr) <= 3) report
let check_report_safety report =
if not (all_increasing report || all_decreasing report) then false
else if not (at_least_one report && at_most_three report) then false
else true
let rec count_safe_reports acc lst =
match lst with
| [] -> acc
| h :: t ->
if h then count_safe_reports (acc + 1) t else count_safe_reports acc t
let solve reports =
reports |> List.map check_report_safety |> count_safe_reports 0
let line_to_report line =
line |> String.split_on_char ' ' |> List.map int_of_string
let lines_to_reports lines = List.map line_to_report lines
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