#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]; } long long solve() { long long k = tc.k; long long N2 = (long long)n * n; if (n == 1) return do_query(1, 1); long long heap_k = min(k, N2 - k + 1); if (heap_k + n <= 24000) { if (k <= N2 - k + 1) { priority_queue, vector>, greater<>> pq; vector> vis(n + 1, vector(n + 1, false)); pq.emplace(do_query(1, 1), 1, 1); vis[1][1] = true; long long result = -1; for (long long i = 0; i < k; i++) { auto [v, r, c] = pq.top(); pq.pop(); result = v; if (r+1<=n && !vis[r+1][c]) { vis[r+1][c]=true; pq.emplace(do_query(r+1,c),r+1,c); } if (c+1<=n && !vis[r][c+1]) { vis[r][c+1]=true; pq.emplace(do_query(r,c+1),r,c+1); } } return result; } else { long long kk = N2 - k + 1; priority_queue> pq; vector> vis(n + 1, vector(n + 1, false)); pq.emplace(do_query(n,n),n,n); vis[n][n]=true; long long result = -1; for (long long i = 0; i < kk; i++) { auto [v, r, c] = pq.top(); pq.pop(); result = v; if (r-1>=1 && !vis[r-1][c]) { vis[r-1][c]=true; pq.emplace(do_query(r-1,c),r-1,c); } if (c-1>=1 && !vis[r][c-1]) { vis[r][c-1]=true; pq.emplace(do_query(r,c-1),r,c-1); } } return result; } } // Strategy: query a strategic row entirely, use its sorted values as pivot candidates, // then binary search within these values using staircase walks. // Pick the row at position ceil(k/n) - this row's values span the likely answer range. // Actually, for the first pass, query the row at index ceil(k/n). // Its values range from a[r][1] to a[r][n], and the k-th element should be // somewhere in or near this range. vector jLo(n + 1, 0), jHi(n + 1, n); long long cLo = 0, cHi = N2; // Query a strategic row int pivot_row = max(1, min(n, (int)((k + n - 1) / n))); // Query the entire row vector row_vals(n + 1); for (int j = 1; j <= n; j++) { row_vals[j] = do_query(pivot_row, j); } // Row values are sorted (by matrix property) // Binary search within this row's values for the right pivot int lo_idx = 1, hi_idx = n; while (lo_idx <= hi_idx && cHi - cLo > 0) { int mid_idx = (lo_idx + hi_idx) / 2; long long pivot = row_vals[mid_idx]; // Staircase walk to count <= pivot vector cutoff(n + 1, 0); long long cnt = 0; int j = jHi[1]; for (int i = 1; i <= n; i++) { int lo_j = jLo[i]; int hi_j = jHi[i]; if (hi_j <= lo_j) { cutoff[i] = lo_j; cnt += lo_j; continue; } if (j > hi_j) j = hi_j; while (j > lo_j && do_query(i, j) > pivot) j--; if (j > lo_j) { cutoff[i] = j; cnt += j; } else { cutoff[i] = lo_j; cnt += lo_j; } } if (cnt >= k) { jHi = cutoff; cHi = cnt; hi_idx = mid_idx - 1; } else { jLo = cutoff; cLo = cnt; lo_idx = mid_idx + 1; } // Check if we can enumerate long long W = cHi - cLo; long long budget = 49500 - query_count; if (W <= budget) break; } // If still too large, query another row and refine further // Find a row with the most remaining candidates while (true) { long long W = cHi - cLo; long long budget = 49500 - query_count; if (W <= budget) break; if (budget < 2 * n + 100) break; // can't afford more walks // Pick a new pivot row: the row with maximum width in current band int best_row = -1, best_width = 0; for (int i = 1; i <= n; i++) { int w = jHi[i] - jLo[i]; if (w > best_width) { best_width = w; best_row = i; } } if (best_row == -1 || best_width == 0) break; // Query the entire active segment of this row for (int j = jLo[best_row] + 1; j <= jHi[best_row]; j++) do_query(best_row, j); // Binary search within this row's active segment int lo_j = jLo[best_row] + 1, hi_j = jHi[best_row]; // Find the value at the right quantile long long need_rank = k - cLo; // rank within current band double frac = (double)need_rank / W; int target_col = lo_j + (int)(frac * (hi_j - lo_j)); target_col = max(lo_j, min(hi_j, target_col)); long long pivot = do_query(best_row, target_col); // Staircase walk vector cutoff(n + 1, 0); long long cnt = 0; int j = jHi[1]; for (int i = 1; i <= n; i++) { int lo_jj = jLo[i], hi_jj = jHi[i]; if (hi_jj <= lo_jj) { cutoff[i] = lo_jj; cnt += lo_jj; continue; } if (j > hi_jj) j = hi_jj; while (j > lo_jj && do_query(i, j) > pivot) j--; if (j > lo_jj) { cutoff[i] = j; cnt += j; } else { cutoff[i] = lo_jj; cnt += lo_jj; } } if (cnt >= k) { jHi = cutoff; cHi = cnt; } else { jLo = cutoff; cLo = cnt; } } // Enumerate remaining long long W = cHi - cLo; long long rank = k - cLo; if (W <= 0) return do_query(1, 1); // shouldn't happen vector cand; cand.reserve((size_t)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 <= 0 || cand.empty()) return do_query(1, 1); if (rank > (long long)cand.size()) return do_query(n, n); 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); } }