Submission #974311

#	Time	Username	Problem	Language	Result	Execution time	Memory
974311		Pannda	Sequence (APIO23_sequence)	C++17	40 / 100	2103 ms	51536 KiB

sequence

#include "sequence.h"

#include <bits/stdc++.h>
using namespace std;

int sequence(int n, vector<int> a) {
    vector<vector<int>> mp(n);
    for (int i = 0; i < n; i++) {
        a[i]--;
        mp[a[i]].push_back(i);
    }

    auto ok = [&](int x) -> bool {
        for (int med = 0; med < n; med++) {
            if (mp[med].empty()) continue;

            vector<int> cnt(n + 1, 0);
            vector<int> le_lr(n + 1, 0), mx_le_lr(n + 1, 0);
            vector<int> le_rl(n + 1, 0), mx_le_rl(n + 1, 0);
            vector<int> ge_lr(n + 1, 0), mx_ge_lr(n + 1, 0);
            vector<int> ge_rl(n + 1, 0), mx_ge_rl(n + 1, 0);
            for (int i = 0; i < n; i++) {
                cnt[i + 1] = cnt[i] + (a[i] <= med);
                le_lr[i + 1] = le_lr[i] + 2 * (a[i] <= med) - 1;
                ge_lr[i + 1] = ge_lr[i] + 2 * (a[i] >= med) - 1;
            }
            for (int i = n - 1; i >= 0; i--) {
                le_rl[i] = le_rl[i + 1] + 2 * (a[i] <= med) - 1;
                ge_rl[i] = ge_rl[i + 1] + 2 * (a[i] >= med) - 1;
            }
            mx_le_lr[n] = le_lr[n], mx_ge_lr[n] = ge_lr[n];
            for (int i = n - 1; i >= 0; i--) {
                mx_le_lr[i] = max(le_lr[i], mx_le_lr[i + 1]);
                mx_ge_lr[i] = max(ge_lr[i], mx_ge_lr[i + 1]);
            }
            mx_le_rl[0] = le_rl[0], mx_ge_rl[0] = ge_rl[0];
            for (int i = 1; i <= n; i++) {
                mx_le_rl[i] = max(le_rl[i], mx_le_rl[i - 1]);
                mx_ge_rl[i] = max(ge_rl[i], mx_ge_rl[i - 1]);
            }

            for (int ii = 0; ii + x <= mp[med].size(); ii++) {
                int l = mp[med][ii];
                int r = mp[med][ii + x - 1] + 1;
                int lem = cnt[r] - cnt[l];
                int gem = (r - l) - lem + x;
                if (2 * lem >= r - l && 2 * gem >= r - l) return true;
                if (2 * lem < r - l) {
                    int val = 2 * lem - r + l; // < 0
                    int up = mx_le_lr[r] - le_lr[r] + mx_le_rl[l] - le_rl[l];
                    if (val + up >= 0) return true;
                } else {
                    int val = 2 * gem - r + l; // < 0
                    int up = mx_ge_lr[r] - ge_lr[r] + mx_ge_rl[l] - ge_rl[l];
                    if (val + up >= 0) return true;
                }
            }
        }
        return false;
    };

    int ans = [&]() -> int {
        int l = 1, r = n;
        while (l < r) {
            int m = (l + r + 1) >> 1;
            if (ok(m)) {
                l = m;
            } else {
                r = m - 1;
            }
        }
        return l;
    }();

    return ans;
}

Compilation message (stderr)

sequence.cpp: In lambda function:
sequence.cpp:42:37: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   42 |             for (int ii = 0; ii + x <= mp[med].size(); ii++) {
      |                              ~~~~~~~^~~~~~~~~~~~~~~~~

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