Submission #951418

#	Time	Username	Problem	Language	Result	Execution time	Memory
951418		vjudge1	Election (BOI18_election)	C++17	0 / 100	2 ms	856 KiB

election

#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const int N = 5e5 + 5;
const int M = 19;

int solve(vector<int> a, int i, int cnt, int bal, vector<int> res) {
    if (i == a.size()) {
        int rev_bal = 0;
        for (int i = res.size() - 1; i; i--) {
            rev_bal += res[i];
            if (rev_bal < 0)
                return 1e9;
        }
        return cnt;
    }
    int ans = 1e9;
    if (a[i] == 1) {
        res.push_back(1);
        ans = min(ans, solve(a, i + 1, cnt, bal + 1, res));
    } else {
        ans = min(ans, solve(a, i + 1, cnt + 1, bal, res));
        if (bal > 0) {
            res.push_back(-1);
            ans = min(ans, solve(a, i + 1, cnt, bal - 1, res));
        }
    }
    return ans;
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    srand(time(0));
    int n = 50;
    cin >> n;
    string s; //"TTCTCC";
    // for (int i = 0; i < n; i++) {
    //     s += rand() % 2 ? 'C' : 'T';
    // }
    cin >> s;
    vector<int> a(n + 1);
    for (int i = 1; i <= n; i++) {
        char c = s[i - 1];
        a[i] = 1 - 2 * (c == 'T');
    }
    vector<int> pre(n + 1), suf(n + 2);
    for (int i = 1; i <= n; i++) {
        pre[i] = pre[i - 1] + a[i];
    }
    for (int i = n; i; i--) {
        suf[i] = suf[i + 1] + a[i];
    }

    vector<int> pos(2 * n + 5, n + 1);
    vector<vector<int>> nxt(n + 2, vector<int>(M, n + 1));
    for (int i = n; i >= 0; i--) {
        int tar = pre[i] - 1 - (a[i] == 1);
        nxt[i][0] = pos[tar + n + 2];
        pos[pre[i] + n + 2] = i;
    }
    for (int j = 1; j < M; j++) {
        for (int i = 0; i <= n; i++) {
            nxt[i][j] = nxt[nxt[i][j - 1]][j - 1];
        }
    }

    pos.assign(2 * n + 5, 0);
    vector<vector<int>> prev(n + 2, vector<int>(M));
    for (int i = 1; i <= n + 1; i++) {
        int tar = suf[i] - 1 - (a[i] == 1);
        prev[i][0] = pos[tar + n + 2];
        pos[suf[i] + n + 2] = i;
    }
    for (int j = 1; j < M; j++) {
        for (int i = 1; i <= n + 1; i++) {
            prev[i][j] = prev[prev[i][j - 1]][j - 1];
        }
    }

    auto get_l_info = [&](int l, int r) -> array<int, 2> {
        if (a[l] == 1)
            l = nxt[l][0];
        int cnt = 0;
        for (int i = M - 1; i >= 0; i--) {
            if (nxt[l][i] <= r) {
                l = nxt[l][i];
                cnt += 1 << i;
            }
        }
        return {l, cnt + (l <= r)};
    };
    auto get_r_info = [&](int l, int r) -> array<int, 2> {
        if (a[r] == 1)
            r = prev[r][0];
        int cnt = 0;
        for (int i = M - 1; i >= 0; i--) {
            if (prev[r][i] >= l) {
                r = prev[r][i];
                cnt += 1 << i;
            }
        }
        return {r, cnt + (l <= r)};
    };

    int q = 1;
    cin >> q;
    while (q--) {
        int l = 1, r = n;
        cin >> l >> r;

        auto l1 = get_l_info(l, r);
        auto r1 = get_r_info(l, r);
        if (l1[0] < r1[0]) {
            cout << l1[1] + r1[1] << "\n";
            continue;
        }
        auto l2 = get_l_info(l, min(l1[0], r1[0]) - 1);
        auto r2 = get_r_info(max(l1[0], r1[0]) + 1, r);
        int ans = l2[1] + r2[1];
        ans += max(l1[1] - l2[1], r1[1] - r2[1]);
        cout << ans << "\n";
        // int ans2 = solve(a, 1, 0, 0, {});
        // if (ans != ans2) {
        //     cout << s << "\n";
        //     cout << l1[0] << " " << l1[1] << " " << r1[0] << " " << r1[1] << "\n";
        //     cout << l2[0] << " " << l2[1] << " " << r2[0] << " " << r2[1] << "\n";
        //     cout << ans << " " << ans2 << "\n";
        // }
    }
}

Compilation message (stderr)

election.cpp: In function 'int solve(std::vector<int>, int, int, int, std::vector<int>)':
election.cpp:10:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |     if (i == a.size()) {
      |         ~~^~~~~~~~~~~

• Subtask 1: 0 / 28
• Subtask 2: 0 / 54
• Subtask 3: 0 / 18