/* 

  Advent of Code 2023 Day 9 in Picat.

  https://adventofcode.com/2023/day/9


  This program was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import util.

main => go.

/*
  $ hyperfine 'picat 9.pi'
  Benchmark 1: picat 9.pi
    Time (mean ± σ):      46.5 ms ±   7.9 ms    [User: 32.9 ms, System: 13.6 ms]
    Range (min … max):    22.3 ms …  59.3 ms    55 runs
*/
go ?=>
  File = "9.txt",
  Nss = [Line.split(" ").map(to_int) : Line in read_file_lines(File)],
  member(Part,1..2),
  Sum = 0,
  foreach(Ns in Nss)
    Ds = diffs(Ns),
    Dss = [Ds],
    while (Ds.remove_dups.len > 1)
      Ds := Ds.diffs,
      Dss := Dss ++ [Ds]
    end,
    if Part == 1 then
      TT = Ns.last + sum([D.last : D in Dss.reverse])
    else
      T = 0,
      foreach(D in Dss.reverse)
        T := D.first - T
      end,
      TT = Ns.first - T
    end,
    Sum := Sum + TT    
  end,
  println(Sum),
  fail.
go => true.

diffs(L) = [L[I]-L[I-1] : I in 2..L.len].