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| using namespace std; | |
| struct TestCase { | |
| int n; | |
| long long k; | |
| vector<vector<long long>> A; | |
| long long answer; | |
| }; | |
| mt19937_64 rng_gen(42); | |
| TestCase gen_matrix(int n, long long k, function<long long(int,int)> valfn) { | |
| TestCase tc; | |
| tc.n = n; tc.k = k; | |
| tc.A.assign(n+1, vector<long long>(n+1, 0)); | |
| vector<long long> 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<long long>(n+1, 0)); | |
| long long C = 1000000, D = 1000; | |
| for (int i = 1; i <= n; i++) | |
| for (int j = 1; j <= n; j++) | |
| tc.A[i][j] = (long long)i * C + (long long)j * D + (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<long long> 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<long long> 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]; | |
| } | |
| // count_leq with staircase walk, returns count and boundary positions | |
| long long count_leq(long long x, vector<int>& pos) { | |
| pos.assign(n + 1, 0); | |
| long long cnt = 0; | |
| int j = n; | |
| for (int i = 1; i <= n; i++) { | |
| while (j >= 1 && do_query(i, j) > x) j--; | |
| pos[i] = j; | |
| cnt += j; | |
| if (j == 0) break; | |
| } | |
| return cnt; | |
| } | |
| long long count_lt(long long x, vector<int>& pos) { | |
| pos.assign(n + 1, 0); | |
| long long cnt = 0; | |
| int j = n; | |
| for (int i = 1; i <= n; i++) { | |
| while (j >= 1 && do_query(i, j) >= x) j--; | |
| pos[i] = j; | |
| cnt += j; | |
| if (j == 0) break; | |
| } | |
| return cnt; | |
| } | |
| long long solve() { | |
| long long k = tc.k; | |
| long long N2 = (long long)n * n; | |
| if (n == 1) return do_query(1, 1); | |
| if (k == 1) return do_query(1, 1); | |
| if (k == N2) return do_query(n, n); | |
| long long heap_k = min(k, N2 - k + 1); | |
| if (heap_k + n <= 24000) { | |
| if (k <= N2 - k + 1) { | |
| priority_queue<tuple<long long, int, int>, vector<tuple<long long, int, int>>, 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 = N2 - k + 1; | |
| priority_queue<tuple<long long, int, int>> 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; | |
| } | |
| } | |
| // Strategy: query a strategic row, then use binary search on values from that row | |
| // Row sqrt(k) should contain values near the k-th smallest | |
| // Actually: query row n/2. The median row has n values spanning roughly | |
| // from a[n/2][1] to a[n/2][n]. Binary search within this row to find approximate pivot. | |
| // Better strategy: query the anti-diagonal elements to get initial value range, | |
| // then do value-based binary search with staircase count_leq | |
| // Phase 1: Get bounds. | |
| // Row ceil(k/n) column n is an upper bound for the k-th element. | |
| int rBound = min(n, (int)((k + n - 1) / n)); | |
| long long hi = do_query(rBound, n); | |
| long long lo = do_query(1, 1); | |
| // Verify: count_leq(hi) >= k | |
| vector<int> posHi; | |
| long long cntHi = count_leq(hi, posHi); | |
| if (cntHi < k) { | |
| hi = do_query(n, n); | |
| cntHi = count_leq(hi, posHi); | |
| } | |
| vector<int> posLo; | |
| long long cntLo = 0; | |
| // posLo is all zeros initially | |
| posLo.assign(n + 1, 0); | |
| // Phase 2: Narrow via value-based binary search | |
| // Each count_leq costs O(n) but caches queries | |
| // Use the row-merge approach: query a strategic row and binary search within it | |
| // Better: use the "fractional cascading" idea. | |
| // Query row at index ceil(sqrt(n)) and use values from that row as candidates. | |
| // Actually, let's use a simpler approach: | |
| // Binary search: find min value v such that count_leq(v) >= k | |
| // But we can't binary search on long long values directly (range too large) | |
| // Instead, generate candidate values by querying strategic positions | |
| // Strategy: Query entire row at index ~sqrt(k/n) * something | |
| // Actually the simplest approach that works: | |
| // Use the quickselect approach but with the staircase from TOP (i ascending, j descending) | |
| // and use value from the staircase boundary as next pivot | |
| // Let me implement: quickselect with staircase walk, and use boundary values | |
| // as pivot candidates for next iteration | |
| for (int iter = 0; iter < 50; iter++) { | |
| long long candTotal = cntHi - cntLo; | |
| if (candTotal <= 0) return hi; | |
| long long needSmall = k - cntLo; | |
| long long needLarge = cntHi - k + 1; | |
| // Count non-empty segments | |
| int nonempty = 0; | |
| for (int i = 1; i <= n; i++) { | |
| if (posHi[i] > posLo[i]) nonempty++; | |
| } | |
| long long budget = 49500 - query_count; | |
| if (min(needSmall, needLarge) + nonempty + 10 <= budget) { | |
| // Enumerate | |
| if (needSmall <= needLarge) { | |
| priority_queue<tuple<long long, int, int>, vector<tuple<long long, int, int>>, greater<>> pq; | |
| for (int i = 1; i <= n; i++) { | |
| int L = posLo[i] + 1, R = posHi[i]; | |
| if (L >= 1 && L <= n && L <= R) pq.emplace(do_query(i, L), i, L); | |
| } | |
| long long result = 0; | |
| for (long long t = 0; t < needSmall; t++) { | |
| auto [v, r, c] = pq.top(); pq.pop(); | |
| result = v; | |
| if (c + 1 <= posHi[r]) pq.emplace(do_query(r, c + 1), r, c + 1); | |
| } | |
| return result; | |
| } else { | |
| priority_queue<tuple<long long, int, int>> pq; | |
| for (int i = 1; i <= n; i++) { | |
| int L = posLo[i] + 1, R = posHi[i]; | |
| if (R >= 1 && R <= n && L <= R) pq.emplace(do_query(i, R), i, R); | |
| } | |
| long long result = 0; | |
| for (long long t = 0; t < needLarge; t++) { | |
| auto [v, r, c] = pq.top(); pq.pop(); | |
| result = v; | |
| if (c - 1 >= posLo[r] + 1) pq.emplace(do_query(r, c - 1), r, c - 1); | |
| } | |
| return result; | |
| } | |
| } | |
| if (budget < 2 * n + 200) return hi; // fallback | |
| // Choose pivot: query a strategic position | |
| // Use the median row's value at the fractional position | |
| // The "median row" in terms of width-weighted is more complex | |
| // Simple approach: pick the row with the most candidates and query at target_frac | |
| // Build prefix sums for position-uniform sampling | |
| vector<long long> pref(n + 1, 0); | |
| for (int i = 1; i <= n; i++) { | |
| int len = posHi[i] - posLo[i]; | |
| pref[i] = pref[i - 1] + max(0, len); | |
| } | |
| candTotal = pref[n]; | |
| if (candTotal <= 0) return hi; | |
| // Sample multiple pivot candidates from the boundary values | |
| // After a staircase walk for count_leq(v), the cells a[i][posHi[i]] are all <= hi | |
| // and cells a[i][posHi[i]+1] (if exists) are > hi. | |
| // The boundary values a[i][posHi[i]] and a[i][posLo[i]+1] are in the cache. | |
| // Let's use the midpoint of each segment as pivot candidate. | |
| // Actually, let me try: query the midpoint of each active segment in value terms. | |
| // For row i, the values range from a[i, posLo[i]+1] to a[i, posHi[i]]. | |
| // The midpoint (in position) is (posLo[i]+1+posHi[i])/2. | |
| // Sample from several rows, pick weighted quantile. | |
| double target_q = (double)needSmall / (double)candTotal; | |
| // Sample from ALL active rows at the target_q position | |
| vector<pair<long long, long long>> vw; // (value, weight) | |
| for (int i = 1; i <= n; i++) { | |
| int L = posLo[i] + 1, R = posHi[i]; | |
| if (L > R || L < 1 || R > n) continue; | |
| int width = R - L + 1; | |
| int col = L + (int)(target_q * max(0, width - 1)); | |
| col = max(L, min(R, col)); | |
| vw.push_back({do_query(i, col), width}); | |
| } | |
| // Weighted quantile | |
| sort(vw.begin(), vw.end()); | |
| long long target_w = (long long)(target_q * candTotal); | |
| long long cum = 0; | |
| long long pivot = vw.back().first; | |
| for (auto& [v, w] : vw) { | |
| cum += w; | |
| if (cum >= target_w) { | |
| pivot = v; | |
| break; | |
| } | |
| } | |
| // Staircase walk for pivot | |
| vector<int> posPivot; | |
| long long cntPivot = count_leq(pivot, posPivot); | |
| if (cntPivot >= k) { | |
| if (cntPivot == cntHi && pivot >= hi) { | |
| // Pivot didn't help - try count_lt | |
| vector<int> posLess; | |
| long long cntLess = count_lt(pivot, posLess); | |
| if (cntLess < k) return pivot; // answer is pivot | |
| hi = pivot - 1; // This is a hack for integer values | |
| posHi = posLess; | |
| cntHi = cntLess; | |
| } else { | |
| hi = pivot; | |
| posHi = posPivot; | |
| cntHi = cntPivot; | |
| } | |
| } else { | |
| cntLo = cntPivot; | |
| posLo = posPivot; | |
| lo = pivot; | |
| } | |
| } | |
| return -1; | |
| } | |
| }; | |
| int main() { | |
| struct TestDef { | |
| string name; | |
| function<TestCase()> gen; | |
| }; | |
| vector<TestDef> tests; | |
| tests.push_back({"additive n=100 k=5000", []{ return gen_additive(100, 5000); }}); | |
| tests.push_back({"multiplicative 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({"multiplicative 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({"multiplicative 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({"multiplicative n=2000 k=100000", []{ return gen_multiplicative(2000, 100000); }}); | |
| tests.push_back({"multiplicative 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); | |
| double score; | |
| int used = s.query_count; | |
| if (!correct) score = 0.0; | |
| else if (used <= tc.n) score = 1.0; | |
| else if (used >= 50000) score = 0.0; | |
| else score = (50000.0 - used) / (50000.0 - tc.n); | |
| printf("%-45s n=%4d k=%8lld queries=%6d correct=%s score=%.4f\n", | |
| t.name.c_str(), tc.n, tc.k, used, correct ? "YES" : "NO", score); | |
| } | |
| return 0; | |
| } | |