#include "sequence.h"
#include <bits/stdc++.h>
#define SZ(s) ((int) ((s).size()))
using namespace std;
vector<int> medians(const vector<int> values) {
int n = SZ(values);
assert(n > 0);
if (n % 2 == 0) {
return {values[n/2 - 1], values[n / 2]};
} else {
return {values[n/2]};
}
}
int sub1(const vector<int>& a) {
int n = SZ(a);
int res = 0;
for (int l = 0; l < n; ++l) {
for (int r = l; r < n; ++r) {
vector<int> b(a.begin() + l, a.begin() + r + 1);
unordered_map<int, int> cnt;
for (int val : b) cnt[val] += 1;
sort(b.begin(), b.end());
auto meds = medians(b);
for (int med : meds) {
res = max(res, cnt[med]);
}
}
}
return res;
}
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
using namespace __gnu_pbds;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
using namespace __gnu_pbds;
int sub2(const vector<int>& a) {
int n = SZ(a);
int res = 0;
for (int l = 0; l < n; ++l) {
unordered_map<int, int> cnt;
ordered_set values;
for (int r = l; r < n; ++r) {
cnt[a[r]]++;
values.insert(a[r]);
int k = SZ(values);
if (k % 2 == 0) {
res = max(res, cnt[*values.find_by_order(k / 2 - 1)]);
res = max(res, cnt[*values.find_by_order(k / 2)]);
} else {
res = max(res, cnt[*values.find_by_order(k / 2)]);
}
}
}
return res;
}
bool is_sub_3(const std::vector<int> a) {
auto mit = max_element(a.begin(), a.end());
return std::is_sorted(a.begin(), mit)
&& std::is_sorted(mit, a.end(), std::greater<int>());
}
int len(const std::pair<int,int>& p) {
return p.second - p.first + 1;
}
bool can_be_median(int cnt_less, int cnt_equal, int cnt_greater) {
return cnt_equal + cnt_less >= cnt_greater;
}
int sub3(const vector<int>& a) {
int n = SZ(a);
unordered_map<int, vector<pair<int,int>>> pos;
int l = 0;
while (l < n) {
int r = l;
while (r < n && a[l] == a[r]) ++r;
pos[a[l]].emplace_back(l, r-1);
l = r;
}
int res = 0;
for (const auto& [val, lrs] : pos) {
// only 1 segment
for (const auto& lr : lrs) res = max(res, len(lr));
// 2 segments
if (SZ(lrs) < 2) continue;
assert(SZ(lrs) == 2);
int cnt_equal = len(lrs[0]) + len(lrs[1]);
int cnt_greater = len({lrs[0].second + 1, lrs[1].first - 1});
int cnt_less = len({0, lrs[0].first - 1}) + len({lrs[1].second + 1, n-1});
if (can_be_median(cnt_less, cnt_equal, cnt_greater)) {
res = max(res, cnt_equal);
}
}
return res;
}
int sub4(const vector<int>& a) {
int n = SZ(a);
vector<vector<int>> cnt(3, vector<int> (n, 0));
for (int val = 0; val < 3; ++val) {
for (int i = 0; i < n; ++i) {
if (i) cnt[val][i] = cnt[val][i-1];
cnt[val][i] += (val+1) == a[i];
}
}
for (int l = 0; l < n; ++l) {
}
}
int sequence(int n, std::vector<int> a) {
if (is_sub_3(a)) return sub3(a);
if (*max_element(a.begin(), a.end()) <= 3) return sub4(a);
if (n <= 2000) return sub2(a);
return 0;
}
