#include "dzilib.h" #include <bits/stdc++.h> using std::vector; using u32 = std::uint32_t; using u64 = std::uint64_t; #define DEBUG(x) std::cerr << "Line " << __LINE__ << ": " << #x << " = " << x << "\n" #define TRACE(x) std::cerr << "Line " << __LINE__ << ": " << #x "\n" // Configuration. constexpr bool randomize_offset = true; constexpr u64 randomize_offset_limit = 10; constexpr u64 rng_nonce = 0; const u64 solve_primes[] = {2, 3}; // 200 MB constexpr u64 divisor_limit = 50'000'000; // must be > 10^(17/3), 1e6+ OK u64 choose_brute_limit(const u64 max_n, const u64 max_questions_per_test_case) { if (max_n <= 1'000'000'000 || max_questions_per_test_case >= 130) { return 500'000; } else if (max_questions_per_test_case >= 82) { return 2'000'000; } else if (max_questions_per_test_case >= 75) { return 4'000'000; } else { return 5'000'000; } } /// ================================= const std::uint32_t secret_key[8] = { 235542195, 2150993683, 4252960442, 2004619671, 1424085794, 3389625356, 3726775613, 3633112236 }; namespace chacha_private { template <int shift> void rotate_left(std::uint32_t &x) { x = (x << shift) | (x >> (32 - shift)); } inline void quarter_round(std::uint32_t &a, std::uint32_t &b, std::uint32_t &c, std::uint32_t &d) { a += b; d ^= a; rotate_left<16>(d); c += d; b ^= c; rotate_left<12>(b); a += b; d ^= a; rotate_left<8>(d); c += d; b ^= c; rotate_left<7>(b); } } template<int rounds> void chacha(const std::uint32_t (&key)[8], const std::uint64_t nonce, const std::uint64_t counter, std::uint32_t (&output)[16]) { static_assert(rounds == 8 || rounds == 12 || rounds == 20); using namespace chacha_private; std::uint32_t input[16]; std::memcpy(input + 0, "expand 32-byte k", 4 * sizeof(std::uint32_t)); std::memcpy(input + 4, key, 8 * sizeof(std::uint32_t)); std::memcpy(input + 12, &counter, 2 * sizeof(std::uint32_t)); std::memcpy(input + 14, &nonce, 2 * sizeof(std::uint32_t)); std::uint32_t x[16]; std::memcpy(x, input, 16 * sizeof(std::uint32_t)); for (int double_round = 0; double_round < rounds / 2; ++double_round) { quarter_round(x[0], x[4], x[8], x[12]); quarter_round(x[1], x[5], x[9], x[13]); quarter_round(x[2], x[6], x[10], x[14]); quarter_round(x[3], x[7], x[11], x[15]); quarter_round(x[0], x[5], x[10], x[15]); quarter_round(x[1], x[6], x[11], x[12]); quarter_round(x[2], x[7], x[8], x[13]); quarter_round(x[3], x[4], x[9], x[14]); } for (int i = 0; i < 16; ++i) { x[i] += input[i]; } std::memcpy(output, x, 16 * sizeof(std::uint32_t)); } class ChachaRandom { public: using result_type = std::uint32_t; static constexpr result_type min() { return 0; } static constexpr result_type max() { return std::numeric_limits<result_type>::max(); } explicit ChachaRandom(const std::uint32_t (&key)[8], const std::uint64_t nonce); std::uint32_t operator()() { if (m_buffer_next == 16) { refill_buffer(); } return m_buffer[m_buffer_next++]; } private: void refill_buffer(); std::uint32_t m_chacha_key[8]; std::uint64_t m_chacha_nonce = 0; std::uint64_t m_chacha_counter = 0; std::uint32_t m_buffer[16]; int m_buffer_next = 16; }; ChachaRandom::ChachaRandom(const std::uint32_t (&key)[8], const std::uint64_t nonce) { std::memcpy(m_chacha_key, key, 8 * sizeof(std::uint32_t)); m_chacha_nonce = nonce; } void ChachaRandom::refill_buffer() { chacha<8>(m_chacha_key, m_chacha_nonce, m_chacha_counter++, m_buffer); m_buffer_next = 0; } // ==================================== struct FastDiv { u64 divisor; u64 shift; u64 m; FastDiv(u64 d) { divisor = d; u64 n = 1; while ((u64(1)<<n) < divisor) n += 1; m = (__uint128_t(1) << (64+n)) / divisor + 1; shift = n-1; } std::pair<u64, u64> divrem(u64 a) const { u64 t = (__uint128_t(m) * a) >> 64; u64 q = (t + ((a-t)>>1)) >> shift; u64 r = a - q * divisor; return {q, r}; } }; vector<u32> divisor_table; vector<u32> primes; vector<FastDiv> fast_divs; void compute_primes() { divisor_table.assign(divisor_limit, 0); for (u64 p=2; p < divisor_limit; ++p) { if (divisor_table[p] != 0) continue; primes.push_back(p); fast_divs.push_back(FastDiv(p)); divisor_table[p] = p; for (u64 x = p * p; x < divisor_limit; x += p) { if (divisor_table[x] == 0) { divisor_table[x] = p; } } } } u64 integer_sqrt(const u64 n) { u64 x = u64(std::sqrt(n)); while (x * x > n) --x; while ((x+1) * (x+1) <= n) ++x; return x; } u64 integer_cube_root(const u64 n) { u64 x = u64(std::pow(n, 1.0/3)); while (x * x * x > n) --x; while ((x+1) * (x+1) * (x+1) <= n) ++x; return x; } u64 mult_mod(const u64 a, const u64 b, const u64 m) { return __uint128_t(a) * __uint128_t(b) % m; } u64 power(u64 a, u64 b, u64 m) { u64 res = 1; while (b) { if (b&1u) res = mult_mod(res, a, m); b >>= 1; a = mult_mod(a, a, m); } return res; } bool miller_rabin(const u64 n, const u64 a) { u64 b = n-1; u64 s = 0; while (b%2 == 0) { b /= 2; ++s; } u64 x = power(a, b, n); for (u64 i=0; i<s; ++i) { const u64 y = mult_mod(x, x, n); if (y == 1 && x != 1 && x != n-1) { return false; } x = y; } if (x != 1) return false; return true; } bool large_prime_test(const u64 n) { for (const u64 p : primes) { if (p > 23) break; if (!miller_rabin(n, p)) return false; } return true; } bool is_prime(const u64 n) { if (n < divisor_limit) { return divisor_table[n] == n; } else { return large_prime_test(n); } } u64 compute_num_divisors(u64 n) { u64 result = 1; for (const u64 p : primes) { if (n < divisor_limit || p * p * p > n) break; if (n % p != 0) continue; u64 cnt = 1; n /= p; while (n % p == 0) { ++cnt; n /= p; } result *= (cnt + 1); } while (n > 1 && n < divisor_limit) { const u64 p = divisor_table[n]; u64 cnt = 1; n /= p; while (n % p == 0) { ++cnt; n /= p; } result *= (cnt + 1); } if (n == 1) return result; const u64 a = integer_sqrt(n); if (a * a == n && is_prime(a)) { result *= 3; } else if (is_prime(n)) { result *= 2; } else { // n = p * q result *= 4; } return result; } // Returns 2 if may be false positive. bool check_num_divisors(u64 n, u64 num_divisors) { if (n >= divisor_limit && num_divisors > 3) { u64 p_limit = integer_cube_root(n); for (u64 p_index = 0; p_index < primes.size(); ++p_index) { u64 p = primes[p_index]; if (p > p_limit) break; const FastDiv &fast_div = fast_divs[p_index]; auto [q, rem] = fast_div.divrem(n); if (rem != 0) continue; u64 cnt = 1; n = q; for (;;) { auto [q2, rem2] = fast_div.divrem(n); if (rem2 != 0) break; ++cnt; n = q2; } ++cnt; if (num_divisors % cnt != 0) return false; num_divisors /= cnt; if (n < divisor_limit || num_divisors <= 3) break; p_limit = integer_cube_root(n); } } while (n > 1 && n < divisor_limit) { const u64 p = divisor_table[n]; u64 cnt = 1; n /= p; while (n % p == 0) { ++cnt; n /= p; } ++cnt; if (num_divisors % cnt != 0) return false; num_divisors /= cnt; } if (n == 1) return num_divisors == 1; if (num_divisors < 2 || num_divisors > 4) return false; const u64 a = integer_sqrt(n); if (a * a == n) { return num_divisors == 3; } if (num_divisors == 3) return false; return is_prime(n) == (num_divisors == 2); } u64 brute_compute_num_divisors(const u64 n) { u64 res = 0; u64 d = 1; for (; d*d < n; ++d) { if (n%d == 0) res += 2; } if (d*d==n) res += 1; return res; } bool is_power_of_2(const u32 n) { return n != 0 && (n & (n-1)) == 0; } ChachaRandom rng(secret_key, rng_nonce); constexpr u64 none = -u64(1); u64 max_offset; // n = r (mod m) struct Equation { u64 r; u64 m; }; Equation trivial_equation() { return Equation{0, 1}; } // n = r (mod p^k) struct PowerEquation { u64 r; u64 p; u64 k; }; Equation combine(Equation eq, const PowerEquation peq) { u64 pk = 1; for (u64 k = 1; k <= peq.k; ++k) { pk *= peq.p; while (eq.r % pk != peq.r % pk) { eq.r += eq.m; } eq.m *= peq.p; } return eq; } u64 find_offset_for(const Equation eq) { u64 offset = (eq.m - eq.r) % eq.m; assert(offset <= max_offset); if (randomize_offset) { u64 limit = std::min((max_offset - offset) / eq.m, randomize_offset_limit); std::uniform_int_distribution<u64> dist(0, limit); offset += eq.m * dist(rng); } return offset; } struct QuestionAnswer { u64 offset; u64 num_divisors; u64 difficulty() const { u64 odd_divisors = num_divisors; u64 pow2 = 0; while (odd_divisors % 2 == 0) { odd_divisors /= 2; pow2++; } return -u64(1) - 100 * odd_divisors - pow2; } }; QuestionAnswer ask_random_question() { std::uniform_int_distribution<u64> dist(0, max_offset); QuestionAnswer qa; qa.offset = dist(rng); qa.num_divisors = Ask(qa.offset); return qa; } bool matches(const QuestionAnswer qa, const u64 n) { return check_num_divisors(n + qa.offset, qa.num_divisors); } class PowerSolver { public: explicit PowerSolver(const u64 p_): p(p_) { reset(); } void reset() { options.clear(); step = 1; p_step = p; if (is_power_of_2(k+step+1)) { step = 2; p_step = p * p; } for (u64 s = 0; s < p_step; ++s) { options.emplace(s, none); } refill_shots(); } void refill_shots() { shots_remaining.clear(); for (const auto [s, exception] : options) { for (u64 exc = 0; exc < p; ++exc) { if (exc == exception) continue; shots_remaining.emplace_back(s, exc); } } std::shuffle(shots_remaining.begin(), shots_remaining.end(), rng); } u64 known_range() const { return pk; } PowerEquation knowledge() const { return PowerEquation{r, p, k}; } PowerEquation choose_question() { for (;;) { if (shots_remaining.empty()) { refill_shots(); } const auto [s, exception] = shots_remaining.back(); shots_remaining.pop_back(); const auto it = options.find(s); if (it == options.end()) continue; // We wouldn't put it in the shots list. assert(it->second != exception); return PowerEquation{ r + s * pk + exception * pk * p_step, p, k + step + 1 }; } } // Returns if significant progress. bool process_answer(const PowerEquation eq, const u64 num_divisors) { // If the remainder is valid mod p^(k+2), with one exception mod p^(k+3) we should have: // num_divisors is divisible by (k+3). // If this is not true, then we know an option is invalid. // If it is true, we learn nothing. if (num_divisors % (k + step + 1) == 0) { return false; } assert(eq.p == p && eq.k == k+step+1); const u64 s = eq.r / pk % p_step; const u64 exception = eq.r / (pk * p_step); const auto it = options.find(s); // We wouldn't ask a useless question. assert(it != options.end()); if (it->second == none) { it->second = exception; } else { // We wouln't ask a useless question. assert(it->second != exception); options.erase(it); if (options.size() == 1) { upgrade(); return true; } } return false; } void upgrade() { assert(options.size() == 1); const auto it = options.begin(); const u64 s = it->first; r += s * pk; k += step; pk *= p_step; reset(); } private: // n = remainder (mod p^k) u64 p; u64 p_step; // p^step u64 step; u64 k = 0; u64 r = 0; u64 pk = 1; // p^k // maps s to exception, where: // s < p_step is such that n = r + s * p^k (mod p^(k+step)) // exception < p is such that if s works, then: // n = r + s * p^k + exception * p^(k+step) (mod p^(k+step+1)) // exception can be none std::map<u64, u64> options; vector<std::pair<u64, u64>> shots_remaining; }; class Solver { public: explicit Solver(const u64 max_n1, const u64 brute_limit1) : max_n(max_n1), brute_limit(brute_limit1) { for (const u64 p : solve_primes) { solvers.emplace(p, PowerSolver(p)); } } u64 solve() { phase_1(); generate_n_options(); phase_2(); assert(n_options.size() == 1); return n_options[0]; } private: void phase_1() { for (;;) { if (phase_1_iteration()) { const u64 brute_size = max_n / known_range(); if (brute_size <= brute_limit) { return; } } } } // Returns true if significant progress. bool phase_1_iteration() { const vector<PowerEquation> queries = generate_queries(); Equation equation = trivial_equation(); for (const PowerEquation &query : queries) { equation = combine(equation, query); } const u64 offset = find_offset_for(equation); const u64 num_divisors = Ask(offset); history.push_back(QuestionAnswer{offset, num_divisors}); bool progress = false; for (const PowerEquation &query : queries) { const auto it = solvers.find(query.p); assert(it != solvers.end()); PowerSolver &solver = it->second; if (solver.process_answer(query, num_divisors)) { progress = true; } } return progress; } u64 known_range() const { u64 range = 1; for (const auto &[p, solver] : solvers) { range *= solver.known_range(); } return range; } vector<PowerEquation> generate_queries() { vector<PowerEquation> queries; for (auto &[p, solver] : solvers) { queries.push_back(solver.choose_question()); } return queries; } Equation phase_1_solve() const { Equation total_knowledge = trivial_equation(); for (const auto &[p, solver] : solvers) { const PowerEquation pe = solver.knowledge(); total_knowledge = combine(total_knowledge, pe); } return total_knowledge; } void generate_n_options() { const Equation equation = phase_1_solve(); u64 n = equation.r; if (n == 0) n += equation.m; for (;n <= max_n; n += equation.m) { n_options.push_back(n); } } void phase_2() { std::sort(history.begin(), history.end(), [](const QuestionAnswer a, const QuestionAnswer b) -> bool { return a.difficulty() < b.difficulty(); } ); for (const QuestionAnswer qa : history) { if (n_options.size() <= 1) return; filter_options(qa); } // Very unlikely this will happen. while (n_options.size() > 1) { const QuestionAnswer qa = ask_random_question(); filter_options(qa); } } void filter_options(const QuestionAnswer qa) { auto it = std::remove_if(n_options.begin(), n_options.end(), [qa](const u64 n) -> bool { return !matches(qa, n); } ); n_options.erase(it, n_options.end()); } u64 max_n; u64 brute_limit; std::map<u64, PowerSolver> solvers; vector<QuestionAnswer> history; vector<u64> n_options; }; void test_fast_div() { std::uniform_int_distribution<u64> dist{1, 1000000000000}; std::uniform_int_distribution<u64> dist2{1, 1000000000000000}; for (u64 i=0;i<1000;++i) { u64 d = dist(rng); FastDiv fd(d); u64 n = dist2(rng); assert((fd.divrem(n) == std::pair<u64, u64>{n/d, n%d})); } } void test_num_divisors() { for (u64 n=1; n<=1000000; ++n) { assert(brute_compute_num_divisors(n) == compute_num_divisors(n)); } assert(compute_num_divisors(u64(100000007) * 100000007) == 3); assert(compute_num_divisors(u64(100000007) * 100000037) == 4); assert(compute_num_divisors(100000000000031) == 2); } int main() { compute_primes(); const u64 ntc = GetT(); const u64 max_n = GetN(); const u64 max_questions = GetQ(); max_offset = GetC(); const u64 brute_limit = choose_brute_limit(max_n, max_questions / ntc); for (u64 tc = 0; tc < ntc; ++tc) { Solver solver(max_n, brute_limit); const u64 n = solver.solve(); Answer(n); } }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 | #include "dzilib.h" #include <bits/stdc++.h> using std::vector; using u32 = std::uint32_t; using u64 = std::uint64_t; #define DEBUG(x) std::cerr << "Line " << __LINE__ << ": " << #x << " = " << x << "\n" #define TRACE(x) std::cerr << "Line " << __LINE__ << ": " << #x "\n" // Configuration. constexpr bool randomize_offset = true; constexpr u64 randomize_offset_limit = 10; constexpr u64 rng_nonce = 0; const u64 solve_primes[] = {2, 3}; // 200 MB constexpr u64 divisor_limit = 50'000'000; // must be > 10^(17/3), 1e6+ OK u64 choose_brute_limit(const u64 max_n, const u64 max_questions_per_test_case) { if (max_n <= 1'000'000'000 || max_questions_per_test_case >= 130) { return 500'000; } else if (max_questions_per_test_case >= 82) { return 2'000'000; } else if (max_questions_per_test_case >= 75) { return 4'000'000; } else { return 5'000'000; } } /// ================================= const std::uint32_t secret_key[8] = { 235542195, 2150993683, 4252960442, 2004619671, 1424085794, 3389625356, 3726775613, 3633112236 }; namespace chacha_private { template <int shift> void rotate_left(std::uint32_t &x) { x = (x << shift) | (x >> (32 - shift)); } inline void quarter_round(std::uint32_t &a, std::uint32_t &b, std::uint32_t &c, std::uint32_t &d) { a += b; d ^= a; rotate_left<16>(d); c += d; b ^= c; rotate_left<12>(b); a += b; d ^= a; rotate_left<8>(d); c += d; b ^= c; rotate_left<7>(b); } } template<int rounds> void chacha(const std::uint32_t (&key)[8], const std::uint64_t nonce, const std::uint64_t counter, std::uint32_t (&output)[16]) { static_assert(rounds == 8 || rounds == 12 || rounds == 20); using namespace chacha_private; std::uint32_t input[16]; std::memcpy(input + 0, "expand 32-byte k", 4 * sizeof(std::uint32_t)); std::memcpy(input + 4, key, 8 * sizeof(std::uint32_t)); std::memcpy(input + 12, &counter, 2 * sizeof(std::uint32_t)); std::memcpy(input + 14, &nonce, 2 * sizeof(std::uint32_t)); std::uint32_t x[16]; std::memcpy(x, input, 16 * sizeof(std::uint32_t)); for (int double_round = 0; double_round < rounds / 2; ++double_round) { quarter_round(x[0], x[4], x[8], x[12]); quarter_round(x[1], x[5], x[9], x[13]); quarter_round(x[2], x[6], x[10], x[14]); quarter_round(x[3], x[7], x[11], x[15]); quarter_round(x[0], x[5], x[10], x[15]); quarter_round(x[1], x[6], x[11], x[12]); quarter_round(x[2], x[7], x[8], x[13]); quarter_round(x[3], x[4], x[9], x[14]); } for (int i = 0; i < 16; ++i) { x[i] += input[i]; } std::memcpy(output, x, 16 * sizeof(std::uint32_t)); } class ChachaRandom { public: using result_type = std::uint32_t; static constexpr result_type min() { return 0; } static constexpr result_type max() { return std::numeric_limits<result_type>::max(); } explicit ChachaRandom(const std::uint32_t (&key)[8], const std::uint64_t nonce); std::uint32_t operator()() { if (m_buffer_next == 16) { refill_buffer(); } return m_buffer[m_buffer_next++]; } private: void refill_buffer(); std::uint32_t m_chacha_key[8]; std::uint64_t m_chacha_nonce = 0; std::uint64_t m_chacha_counter = 0; std::uint32_t m_buffer[16]; int m_buffer_next = 16; }; ChachaRandom::ChachaRandom(const std::uint32_t (&key)[8], const std::uint64_t nonce) { std::memcpy(m_chacha_key, key, 8 * sizeof(std::uint32_t)); m_chacha_nonce = nonce; } void ChachaRandom::refill_buffer() { chacha<8>(m_chacha_key, m_chacha_nonce, m_chacha_counter++, m_buffer); m_buffer_next = 0; } // ==================================== struct FastDiv { u64 divisor; u64 shift; u64 m; FastDiv(u64 d) { divisor = d; u64 n = 1; while ((u64(1)<<n) < divisor) n += 1; m = (__uint128_t(1) << (64+n)) / divisor + 1; shift = n-1; } std::pair<u64, u64> divrem(u64 a) const { u64 t = (__uint128_t(m) * a) >> 64; u64 q = (t + ((a-t)>>1)) >> shift; u64 r = a - q * divisor; return {q, r}; } }; vector<u32> divisor_table; vector<u32> primes; vector<FastDiv> fast_divs; void compute_primes() { divisor_table.assign(divisor_limit, 0); for (u64 p=2; p < divisor_limit; ++p) { if (divisor_table[p] != 0) continue; primes.push_back(p); fast_divs.push_back(FastDiv(p)); divisor_table[p] = p; for (u64 x = p * p; x < divisor_limit; x += p) { if (divisor_table[x] == 0) { divisor_table[x] = p; } } } } u64 integer_sqrt(const u64 n) { u64 x = u64(std::sqrt(n)); while (x * x > n) --x; while ((x+1) * (x+1) <= n) ++x; return x; } u64 integer_cube_root(const u64 n) { u64 x = u64(std::pow(n, 1.0/3)); while (x * x * x > n) --x; while ((x+1) * (x+1) * (x+1) <= n) ++x; return x; } u64 mult_mod(const u64 a, const u64 b, const u64 m) { return __uint128_t(a) * __uint128_t(b) % m; } u64 power(u64 a, u64 b, u64 m) { u64 res = 1; while (b) { if (b&1u) res = mult_mod(res, a, m); b >>= 1; a = mult_mod(a, a, m); } return res; } bool miller_rabin(const u64 n, const u64 a) { u64 b = n-1; u64 s = 0; while (b%2 == 0) { b /= 2; ++s; } u64 x = power(a, b, n); for (u64 i=0; i<s; ++i) { const u64 y = mult_mod(x, x, n); if (y == 1 && x != 1 && x != n-1) { return false; } x = y; } if (x != 1) return false; return true; } bool large_prime_test(const u64 n) { for (const u64 p : primes) { if (p > 23) break; if (!miller_rabin(n, p)) return false; } return true; } bool is_prime(const u64 n) { if (n < divisor_limit) { return divisor_table[n] == n; } else { return large_prime_test(n); } } u64 compute_num_divisors(u64 n) { u64 result = 1; for (const u64 p : primes) { if (n < divisor_limit || p * p * p > n) break; if (n % p != 0) continue; u64 cnt = 1; n /= p; while (n % p == 0) { ++cnt; n /= p; } result *= (cnt + 1); } while (n > 1 && n < divisor_limit) { const u64 p = divisor_table[n]; u64 cnt = 1; n /= p; while (n % p == 0) { ++cnt; n /= p; } result *= (cnt + 1); } if (n == 1) return result; const u64 a = integer_sqrt(n); if (a * a == n && is_prime(a)) { result *= 3; } else if (is_prime(n)) { result *= 2; } else { // n = p * q result *= 4; } return result; } // Returns 2 if may be false positive. bool check_num_divisors(u64 n, u64 num_divisors) { if (n >= divisor_limit && num_divisors > 3) { u64 p_limit = integer_cube_root(n); for (u64 p_index = 0; p_index < primes.size(); ++p_index) { u64 p = primes[p_index]; if (p > p_limit) break; const FastDiv &fast_div = fast_divs[p_index]; auto [q, rem] = fast_div.divrem(n); if (rem != 0) continue; u64 cnt = 1; n = q; for (;;) { auto [q2, rem2] = fast_div.divrem(n); if (rem2 != 0) break; ++cnt; n = q2; } ++cnt; if (num_divisors % cnt != 0) return false; num_divisors /= cnt; if (n < divisor_limit || num_divisors <= 3) break; p_limit = integer_cube_root(n); } } while (n > 1 && n < divisor_limit) { const u64 p = divisor_table[n]; u64 cnt = 1; n /= p; while (n % p == 0) { ++cnt; n /= p; } ++cnt; if (num_divisors % cnt != 0) return false; num_divisors /= cnt; } if (n == 1) return num_divisors == 1; if (num_divisors < 2 || num_divisors > 4) return false; const u64 a = integer_sqrt(n); if (a * a == n) { return num_divisors == 3; } if (num_divisors == 3) return false; return is_prime(n) == (num_divisors == 2); } u64 brute_compute_num_divisors(const u64 n) { u64 res = 0; u64 d = 1; for (; d*d < n; ++d) { if (n%d == 0) res += 2; } if (d*d==n) res += 1; return res; } bool is_power_of_2(const u32 n) { return n != 0 && (n & (n-1)) == 0; } ChachaRandom rng(secret_key, rng_nonce); constexpr u64 none = -u64(1); u64 max_offset; // n = r (mod m) struct Equation { u64 r; u64 m; }; Equation trivial_equation() { return Equation{0, 1}; } // n = r (mod p^k) struct PowerEquation { u64 r; u64 p; u64 k; }; Equation combine(Equation eq, const PowerEquation peq) { u64 pk = 1; for (u64 k = 1; k <= peq.k; ++k) { pk *= peq.p; while (eq.r % pk != peq.r % pk) { eq.r += eq.m; } eq.m *= peq.p; } return eq; } u64 find_offset_for(const Equation eq) { u64 offset = (eq.m - eq.r) % eq.m; assert(offset <= max_offset); if (randomize_offset) { u64 limit = std::min((max_offset - offset) / eq.m, randomize_offset_limit); std::uniform_int_distribution<u64> dist(0, limit); offset += eq.m * dist(rng); } return offset; } struct QuestionAnswer { u64 offset; u64 num_divisors; u64 difficulty() const { u64 odd_divisors = num_divisors; u64 pow2 = 0; while (odd_divisors % 2 == 0) { odd_divisors /= 2; pow2++; } return -u64(1) - 100 * odd_divisors - pow2; } }; QuestionAnswer ask_random_question() { std::uniform_int_distribution<u64> dist(0, max_offset); QuestionAnswer qa; qa.offset = dist(rng); qa.num_divisors = Ask(qa.offset); return qa; } bool matches(const QuestionAnswer qa, const u64 n) { return check_num_divisors(n + qa.offset, qa.num_divisors); } class PowerSolver { public: explicit PowerSolver(const u64 p_): p(p_) { reset(); } void reset() { options.clear(); step = 1; p_step = p; if (is_power_of_2(k+step+1)) { step = 2; p_step = p * p; } for (u64 s = 0; s < p_step; ++s) { options.emplace(s, none); } refill_shots(); } void refill_shots() { shots_remaining.clear(); for (const auto [s, exception] : options) { for (u64 exc = 0; exc < p; ++exc) { if (exc == exception) continue; shots_remaining.emplace_back(s, exc); } } std::shuffle(shots_remaining.begin(), shots_remaining.end(), rng); } u64 known_range() const { return pk; } PowerEquation knowledge() const { return PowerEquation{r, p, k}; } PowerEquation choose_question() { for (;;) { if (shots_remaining.empty()) { refill_shots(); } const auto [s, exception] = shots_remaining.back(); shots_remaining.pop_back(); const auto it = options.find(s); if (it == options.end()) continue; // We wouldn't put it in the shots list. assert(it->second != exception); return PowerEquation{ r + s * pk + exception * pk * p_step, p, k + step + 1 }; } } // Returns if significant progress. bool process_answer(const PowerEquation eq, const u64 num_divisors) { // If the remainder is valid mod p^(k+2), with one exception mod p^(k+3) we should have: // num_divisors is divisible by (k+3). // If this is not true, then we know an option is invalid. // If it is true, we learn nothing. if (num_divisors % (k + step + 1) == 0) { return false; } assert(eq.p == p && eq.k == k+step+1); const u64 s = eq.r / pk % p_step; const u64 exception = eq.r / (pk * p_step); const auto it = options.find(s); // We wouldn't ask a useless question. assert(it != options.end()); if (it->second == none) { it->second = exception; } else { // We wouln't ask a useless question. assert(it->second != exception); options.erase(it); if (options.size() == 1) { upgrade(); return true; } } return false; } void upgrade() { assert(options.size() == 1); const auto it = options.begin(); const u64 s = it->first; r += s * pk; k += step; pk *= p_step; reset(); } private: // n = remainder (mod p^k) u64 p; u64 p_step; // p^step u64 step; u64 k = 0; u64 r = 0; u64 pk = 1; // p^k // maps s to exception, where: // s < p_step is such that n = r + s * p^k (mod p^(k+step)) // exception < p is such that if s works, then: // n = r + s * p^k + exception * p^(k+step) (mod p^(k+step+1)) // exception can be none std::map<u64, u64> options; vector<std::pair<u64, u64>> shots_remaining; }; class Solver { public: explicit Solver(const u64 max_n1, const u64 brute_limit1) : max_n(max_n1), brute_limit(brute_limit1) { for (const u64 p : solve_primes) { solvers.emplace(p, PowerSolver(p)); } } u64 solve() { phase_1(); generate_n_options(); phase_2(); assert(n_options.size() == 1); return n_options[0]; } private: void phase_1() { for (;;) { if (phase_1_iteration()) { const u64 brute_size = max_n / known_range(); if (brute_size <= brute_limit) { return; } } } } // Returns true if significant progress. bool phase_1_iteration() { const vector<PowerEquation> queries = generate_queries(); Equation equation = trivial_equation(); for (const PowerEquation &query : queries) { equation = combine(equation, query); } const u64 offset = find_offset_for(equation); const u64 num_divisors = Ask(offset); history.push_back(QuestionAnswer{offset, num_divisors}); bool progress = false; for (const PowerEquation &query : queries) { const auto it = solvers.find(query.p); assert(it != solvers.end()); PowerSolver &solver = it->second; if (solver.process_answer(query, num_divisors)) { progress = true; } } return progress; } u64 known_range() const { u64 range = 1; for (const auto &[p, solver] : solvers) { range *= solver.known_range(); } return range; } vector<PowerEquation> generate_queries() { vector<PowerEquation> queries; for (auto &[p, solver] : solvers) { queries.push_back(solver.choose_question()); } return queries; } Equation phase_1_solve() const { Equation total_knowledge = trivial_equation(); for (const auto &[p, solver] : solvers) { const PowerEquation pe = solver.knowledge(); total_knowledge = combine(total_knowledge, pe); } return total_knowledge; } void generate_n_options() { const Equation equation = phase_1_solve(); u64 n = equation.r; if (n == 0) n += equation.m; for (;n <= max_n; n += equation.m) { n_options.push_back(n); } } void phase_2() { std::sort(history.begin(), history.end(), [](const QuestionAnswer a, const QuestionAnswer b) -> bool { return a.difficulty() < b.difficulty(); } ); for (const QuestionAnswer qa : history) { if (n_options.size() <= 1) return; filter_options(qa); } // Very unlikely this will happen. while (n_options.size() > 1) { const QuestionAnswer qa = ask_random_question(); filter_options(qa); } } void filter_options(const QuestionAnswer qa) { auto it = std::remove_if(n_options.begin(), n_options.end(), [qa](const u64 n) -> bool { return !matches(qa, n); } ); n_options.erase(it, n_options.end()); } u64 max_n; u64 brute_limit; std::map<u64, PowerSolver> solvers; vector<QuestionAnswer> history; vector<u64> n_options; }; void test_fast_div() { std::uniform_int_distribution<u64> dist{1, 1000000000000}; std::uniform_int_distribution<u64> dist2{1, 1000000000000000}; for (u64 i=0;i<1000;++i) { u64 d = dist(rng); FastDiv fd(d); u64 n = dist2(rng); assert((fd.divrem(n) == std::pair<u64, u64>{n/d, n%d})); } } void test_num_divisors() { for (u64 n=1; n<=1000000; ++n) { assert(brute_compute_num_divisors(n) == compute_num_divisors(n)); } assert(compute_num_divisors(u64(100000007) * 100000007) == 3); assert(compute_num_divisors(u64(100000007) * 100000037) == 4); assert(compute_num_divisors(100000000000031) == 2); } int main() { compute_primes(); const u64 ntc = GetT(); const u64 max_n = GetN(); const u64 max_questions = GetQ(); max_offset = GetC(); const u64 brute_limit = choose_brute_limit(max_n, max_questions / ntc); for (u64 tc = 0; tc < ntc; ++tc) { Solver solver(max_n, brute_limit); const u64 n = solver.solve(); Answer(n); } } |