Submission #798755

#	Time	Username	Problem	Language	Result	Execution time	Memory
798755		fanwen	Sequence (APIO23_sequence)	C++17	35 / 100	547 ms	51232 KiB

sequence

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define MASK(x) (1LL << (x))
#define BIT(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x).begin(), (x).end()
#define REP(i, n) for (int i = 0, _n = n; i < _n; ++i)
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i, a, b) for (int i = (a), _b = (b); i >= _b; --i)
#define FORE(i, a, b) for (int i = (a), _b = (b); i < _b; ++i)
#define debug(...) "[" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
#define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }

template <class A, class B> bool minimize(A &a, B b)  { if (a > b) { a = b; return true; } return false; }
template <class A, class B> bool maximize(A &a, B b)  { if (a < b) { a = b; return true; } return false; }

typedef tree <int, null_type, less_equal <int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

int sub2 (int n, vector <int> a) {
    int res = 0;
    REP(l, n) {
        unordered_map <int, int> cnt;
        ordered_set values;
        FORE(i, l, n) {
            cnt[a[i]]++;
            values.insert(a[i]);
            int k = i - l + 1;
            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;
}

int sub3 (int n, vector <int> a) {
    unordered_map <int, vector <pair <int, int>>> pos;
    for (int l = 0; l < n;) {
        int r = l;
        while(r < n and a[r] == a[l]) ++r;
        pos[a[l]].emplace_back(l, r - 1);
        l = r;
    }
    auto is_median = [&] (int less, int greater, int equal) -> bool {
        return (equal >= greater ? true : (equal + less >= greater));
    };
    int ans = 0;
    for (auto [_, p] : pos) {
        for (auto [l, r] : p) ans = max(ans, r - l + 1);
        if((int) p.size() < 2) continue;
        assert((int) p.size() == 2);
        int equal = p[0].second - p[0].first + 1 + p[1].second - p[1].first + 1;
        int less = p[0].first + n - 1 - p[1].second;
        int greater = p[1].first - p[0].second - 1;
        if(is_median(less, greater, equal)) ans = max(ans, equal);
    }
    return ans;
}

int sequence(int n, vector <int> a) {
    if(n <= 2000) return sub2(n, a);
    return sub3(n, a);
}

#ifdef  LOCAL

#include <cassert>
#include <cstdio>

#include <vector>

int main() {
  int N;
  freopen("TASK.inp", "r", stdin);
  freopen("TASK.out", "w", stdout);
  cin >> N;

  std::vector<int> A(N);
  for (int i = 0; i < N; ++i) {
    cin >> A[i];
  }

  int result = sequence(N, A);
  cout << result;
  return 0;
}

#endif 
// Dream it. Wish it. Do it.

• Subtask 1: 11 / 11
• Subtask 2: 17 / 17
• Subtask 3: 7 / 7
• Subtask 4: 0 / 12
• Subtask 5: 0 / 13
• Subtask 6: 0 / 22
• Subtask 7: 0 / 18