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1fd0050 | 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 | #include <bits/stdc++.h>
using namespace std;
struct TestCase {
int n;
long long k;
vector<vector<long long>> A;
long long answer;
};
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;
}
struct Solver {
const TestCase& tc;
int query_count;
vector<long long> memo;
int n;
// Diagnostics
int num_iters;
vector<int> walk_costs;
vector<int> sample_costs;
vector<long long> cand_sizes;
vector<double> split_ratios;
Solver(const TestCase& t) : tc(t), query_count(0), n(t.n), num_iters(0) {
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<tuple<long long, int, int>, vector<tuple<long long, int, int>>, greater<>> pq;
vector<vector<bool>> vis(n + 1, vector<bool>(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<tuple<long long, int, int>> pq;
vector<vector<bool>> vis(n + 1, vector<bool>(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;
}
}
vector<int> L(n + 1, 1), R(n + 1, n);
long long k_rem = k;
for (int iter = 0; iter < 100; iter++) {
vector<int> active;
long long total_cand = 0;
for (int i = 1; i <= n; i++) {
if (L[i] <= R[i]) {
active.push_back(i);
total_cand += R[i] - L[i] + 1;
}
}
int na = active.size();
if (total_cand == 0) break;
if (total_cand == 1) {
for (int i : active) return do_query(i, L[i]);
break;
}
long long budget = 49500 - query_count;
if (k_rem + na <= budget) {
num_iters = iter;
priority_queue<tuple<long long, int, int>, vector<tuple<long long, int, int>>, greater<>> pq;
for (int i : active) pq.emplace(do_query(i, L[i]), i, L[i]);
for (long long t = 1; t < k_rem; t++) {
auto [v, r, c] = pq.top(); pq.pop();
if (c + 1 <= R[r]) pq.emplace(do_query(r, c + 1), r, c + 1);
}
return get<0>(pq.top());
}
long long rev_k = total_cand - k_rem + 1;
if (rev_k + na <= budget) {
num_iters = iter;
priority_queue<tuple<long long, int, int>> pq;
for (int i : active) pq.emplace(do_query(i, R[i]), i, R[i]);
for (long long t = 1; t < rev_k; t++) {
auto [v, r, c] = pq.top(); pq.pop();
if (c - 1 >= L[r]) pq.emplace(do_query(r, c - 1), r, c - 1);
}
return get<0>(pq.top());
}
int qc_before = query_count;
// Pivot selection (original)
vector<long long> pvals;
double target_frac = (double)(k_rem - 0.5) / total_cand;
int sample_n = max(1, min(na, (int)ceil(sqrt((double)na) * 4)));
int step = max(1, na / sample_n);
for (int idx = 0; idx < na; idx += step) {
int i = active[idx];
int width = R[i] - L[i] + 1;
int col = L[i] + (int)(target_frac * width);
col = max(L[i], min(R[i], col));
pvals.push_back(do_query(i, col));
}
sort(pvals.begin(), pvals.end());
long long pivot = pvals[pvals.size() / 2];
int qc_after_sample = query_count;
vector<int> p_le(n + 1, 0);
{
int j = 0;
for (int idx = na - 1; idx >= 0; idx--) {
int i = active[idx];
j = max(j, L[i]);
while (j <= R[i] && do_query(i, j) <= pivot) j++;
p_le[i] = j - 1;
}
}
int qc_after_walk = query_count;
long long cle = 0;
for (int i : active) {
int rl = min(p_le[i], R[i]);
if (rl >= L[i]) cle += rl - L[i] + 1;
}
double ratio = (double)min(cle, total_cand - cle) / total_cand;
sample_costs.push_back(qc_after_sample - qc_before);
walk_costs.push_back(qc_after_walk - qc_after_sample);
cand_sizes.push_back(total_cand);
split_ratios.push_back(ratio);
if (cle >= k_rem) {
for (int i : active) R[i] = min(R[i], p_le[i]);
} else {
k_rem -= cle;
for (int i : active) L[i] = max(L[i], p_le[i] + 1);
}
}
return -1;
}
};
int main() {
// Test multiplicative n=2000, k=2000000
auto tc = gen_matrix(2000, 2000000, [](int i, int j) -> long long { return (long long)i * j; });
Solver s(tc);
long long result = s.solve();
bool correct = (result == tc.answer);
printf("Result: %lld, Expected: %lld, Correct: %s, Queries: %d\n",
result, tc.answer, correct ? "YES" : "NO", s.query_count);
printf("Iterations before fallback: %d\n", s.num_iters);
printf("\nPer-iteration breakdown:\n");
printf("%-5s %10s %8s %8s %10s\n", "Iter", "Candidates", "Sample", "Walk", "SplitRatio");
for (int i = 0; i < (int)s.walk_costs.size(); i++) {
printf("%-5d %10lld %8d %8d %10.4f\n",
i, s.cand_sizes[i], s.sample_costs[i], s.walk_costs[i], s.split_ratios[i]);
}
// Also test additive
printf("\n--- Additive n=2000 k=2000000 ---\n");
auto tc2 = gen_matrix(2000, 2000000, [](int i, int j) -> long long { return i + j; });
Solver s2(tc2);
long long result2 = s2.solve();
printf("Result: %lld, Expected: %lld, Correct: %s, Queries: %d\n",
result2, tc2.answer, result2 == tc2.answer ? "YES" : "NO", s2.query_count);
printf("Iterations before fallback: %d\n", s2.num_iters);
printf("\nPer-iteration breakdown:\n");
printf("%-5s %10s %8s %8s %10s\n", "Iter", "Candidates", "Sample", "Walk", "SplitRatio");
for (int i = 0; i < (int)s2.walk_costs.size(); i++) {
printf("%-5d %10lld %8d %8d %10.4f\n",
i, s2.cand_sizes[i], s2.sample_costs[i], s2.walk_costs[i], s2.split_ratios[i]);
}
// shifted
printf("\n--- Shifted n=2000 k=2000000 ---\n");
int nn = 2000;
auto tc3 = gen_matrix(nn, 2000000, [nn](int i, int j) -> long long { return (long long)(i + nn) * (j + nn); });
Solver s3(tc3);
long long result3 = s3.solve();
printf("Result: %lld, Expected: %lld, Correct: %s, Queries: %d\n",
result3, tc3.answer, result3 == tc3.answer ? "YES" : "NO", s3.query_count);
printf("Iterations before fallback: %d\n", s3.num_iters);
printf("\nPer-iteration breakdown:\n");
printf("%-5s %10s %8s %8s %10s\n", "Iter", "Candidates", "Sample", "Walk", "SplitRatio");
for (int i = 0; i < (int)s3.walk_costs.size(); i++) {
printf("%-5d %10lld %8d %8d %10.4f\n",
i, s3.cand_sizes[i], s3.sample_costs[i], s3.walk_costs[i], s3.split_ratios[i]);
}
return 0;
}
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