#include using namespace std; struct TestCase { int n; long long k; vector> A; long long answer; }; mt19937_64 rng_gen(42); TestCase gen_matrix(int n, long long k, function valfn) { TestCase tc; tc.n = n; tc.k = k; tc.A.assign(n+1, vector(n+1, 0)); vector all; for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) { tc.A[i][j] = valfn(i, j); all.push_back(tc.A[i][j]); } sort(all.begin(), all.end()); tc.answer = all[k-1]; return tc; } TestCase gen_multiplicative(int n, long long k) { return gen_matrix(n, k, [](int i, int j) -> long long { return (long long)i * j; }); } TestCase gen_shifted(int n, long long k) { return gen_matrix(n, k, [n](int i, int j) -> long long { return (long long)(i + n) * (j + n); }); } TestCase gen_additive(int n, long long k) { return gen_matrix(n, k, [](int i, int j) -> long long { return i + j; }); } TestCase gen_random_sorted(int n, long long k) { TestCase tc; tc.n = n; tc.k = k; tc.A.assign(n+1, vector(n+1, 0)); for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) tc.A[i][j] = (long long)i * 1000000 + (long long)j * 1000 + (rng_gen() % 500); for (int i = 1; i <= n; i++) for (int j = 2; j <= n; j++) tc.A[i][j] = max(tc.A[i][j], tc.A[i][j-1]); for (int j = 1; j <= n; j++) for (int i = 2; i <= n; i++) tc.A[i][j] = max(tc.A[i][j], tc.A[i-1][j]); vector all; for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) all.push_back(tc.A[i][j]); sort(all.begin(), all.end()); tc.answer = all[k-1]; return tc; } struct Solver { const TestCase& tc; int query_count; vector memo; int n; Solver(const TestCase& t) : tc(t), query_count(0), n(t.n) { memo.assign(2002 * 2002, -1); } long long do_query(int r, int c) { int key = r * 2001 + c; if (memo[key] != -1) return memo[key]; query_count++; memo[key] = tc.A[r][c]; return memo[key]; } // Bounded staircase walk: count elements <= mid within jLo..jHi bounds // jLo[i] = last column known to be <= lo_threshold (0 if none) // jHi[i] = last column known to be <= hi_threshold // Returns count and new cutoff positions pair> countLeq(long long mid, const vector& jLo, const vector& jHi) { vector cutoff(n + 1, 0); long long cnt = 0; int j = jHi[1]; // start from upper bound of row 1 if (j > n) j = n; for (int i = 1; i <= n; i++) { int lo = jLo[i]; int hi = jHi[i]; if (hi > n) hi = n; if (lo < 0) lo = 0; if (hi <= lo) { cutoff[i] = lo; cnt += lo; continue; } if (j > hi) j = hi; while (j > lo) { if (do_query(i, j) <= mid) { cutoff[i] = j; cnt += j; goto next_row; } j--; } cutoff[i] = lo; cnt += lo; next_row:; } return {cnt, cutoff}; } long long solve() { long long k = tc.k; long long NLL = (long long)n * n; if (n == 1) return do_query(1, 1); if (k == 1) return do_query(1, 1); if (k == NLL) return do_query(n, n); // For small/extreme k, use heap long long heap_k = min(k, NLL - k + 1); if (heap_k + n <= 24000) { if (k <= NLL - k + 1) { priority_queue, vector>, greater<>> pq; for (int i = 1; i <= n; i++) pq.emplace(do_query(i, 1), i, 1); long long result = -1; for (long long t = 0; t < k; t++) { auto [v, r, c] = pq.top(); pq.pop(); result = v; if (c + 1 <= n) pq.emplace(do_query(r, c + 1), r, c + 1); } return result; } else { long long kk = NLL - k + 1; priority_queue> pq; for (int i = 1; i <= n; i++) pq.emplace(do_query(i, n), i, n); long long result = -1; for (long long t = 0; t < kk; t++) { auto [v, r, c] = pq.top(); pq.pop(); result = v; if (c - 1 >= 1) pq.emplace(do_query(r, c - 1), r, c - 1); } return result; } } // Value-based approach with cached staircase walks vector jLo(n + 1, 0), jHi(n + 1, n); long long cLo = 0, cHi = NLL; // Phase 1: Get initial value bounds // Query a strategic row to get candidate pivot values // Row ceil(k/n) is a good starting point int pivot_row = max(1, min(n, (int)((k + n - 1) / n))); // Query several strategic positions on this row for initial range long long min_val = do_query(1, 1); long long max_val = do_query(n, n); // Quick initial bound: use row pivot_row long long init_hi = do_query(pivot_row, n); auto [ch, cutH] = countLeq(init_hi, jLo, jHi); if (ch >= k) { jHi = cutH; cHi = ch; max_val = init_hi; } // Phase 2: Sample candidate pivot values for binary search // Query along the anti-diagonal and rows to get diverse values set cand_set; // Sample the diagonal for (int i = 1; i <= n; i += max(1, n / 50)) { cand_set.insert(do_query(i, i)); } // Sample the pivot_row for (int j = 1; j <= n; j += max(1, n / 50)) { cand_set.insert(do_query(pivot_row, j)); } // Sample a second row int row2 = max(1, min(n, pivot_row / 2)); for (int j = 1; j <= n; j += max(1, n / 30)) { cand_set.insert(do_query(row2, j)); } int row3 = min(n, pivot_row * 3 / 2); for (int j = 1; j <= n; j += max(1, n / 30)) { cand_set.insert(do_query(row3, j)); } vector candidates(cand_set.begin(), cand_set.end()); sort(candidates.begin(), candidates.end()); // Phase 3: Binary search over candidate values int lo_idx = -1, hi_idx = (int)candidates.size(); int max_walks = max(1, min(20, 40000 / (2 * n))); for (int w = 0; w < max_walks && hi_idx - lo_idx > 1; w++) { int mid_idx = lo_idx + (hi_idx - lo_idx) / 2; long long pivot = candidates[mid_idx]; auto [cnt, cut] = countLeq(pivot, jLo, jHi); if (cnt >= k) { hi_idx = mid_idx; jHi = cut; cHi = cnt; max_val = pivot; } else { lo_idx = mid_idx; jLo = cut; cLo = cnt; min_val = pivot; } long long W = cHi - cLo; long long budget = 49500 - query_count; if (W <= budget) break; } // Phase 4: Numeric binary search if candidate values weren't fine-grained enough int extra_walks = max(1, min(15, (49000 - query_count) / (2 * n))); for (int w = 0; w < extra_walks; w++) { long long W = cHi - cLo; long long budget = 49500 - query_count; if (W <= budget) break; if (min_val >= max_val) break; long long mid_val = min_val + (max_val - min_val) / 2; if (mid_val <= min_val) mid_val = min_val + 1; if (mid_val >= max_val) break; auto [cnt, cut] = countLeq(mid_val, jLo, jHi); if (cnt >= k) { jHi = cut; cHi = cnt; max_val = mid_val; } else { jLo = cut; cLo = cnt; min_val = mid_val; } } // Phase 5: Enumerate long long W = cHi - cLo; long long rank = k - cLo; if (W <= 0 || rank <= 0) return min_val; vector cand; cand.reserve(min((long long)50000, W)); for (int i = 1; i <= n; i++) { for (int j = jLo[i] + 1; j <= jHi[i]; j++) { cand.push_back(do_query(i, j)); } } if (rank > (long long)cand.size()) return max_val; nth_element(cand.begin(), cand.begin() + (rank - 1), cand.end()); return cand[rank - 1]; } }; int main() { struct TestDef { string name; function gen; }; vector tests; tests.push_back({"additive n=100 k=5000", []{ return gen_additive(100, 5000); }}); tests.push_back({"mult n=100 k=5000", []{ return gen_multiplicative(100, 5000); }}); tests.push_back({"additive n=500 k=125000", []{ return gen_additive(500, 125000); }}); tests.push_back({"mult n=500 k=125000", []{ return gen_multiplicative(500, 125000); }}); tests.push_back({"random n=500 k=125000", []{ return gen_random_sorted(500, 125000); }}); tests.push_back({"additive n=2000 k=2000000", []{ return gen_additive(2000, 2000000); }}); tests.push_back({"mult n=2000 k=2000000", []{ return gen_multiplicative(2000, 2000000); }}); tests.push_back({"shifted n=2000 k=2000000", []{ return gen_shifted(2000, 2000000); }}); tests.push_back({"random n=2000 k=2000000", []{ return gen_random_sorted(2000, 2000000); }}); tests.push_back({"mult n=2000 k=100000", []{ return gen_multiplicative(2000, 100000); }}); tests.push_back({"mult n=2000 k=3900000", []{ return gen_multiplicative(2000, 3900000); }}); for (auto& t : tests) { auto tc = t.gen(); Solver s(tc); long long result = s.solve(); bool correct = (result == tc.answer); int used = s.query_count; double score = !correct ? 0.0 : (used <= tc.n ? 1.0 : (used >= 50000 ? 0.0 : (50000.0 - used) / (50000.0 - tc.n))); printf("%-45s q=%6d %s score=%.4f\n", t.name.c_str(), used, correct ? "OK" : "WRONG", score); } }