Submission #306843

#	Time	Username	Problem	Language	Result	Execution time	Memory
306843		MrDomino	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	1080 ms	8184 KiB

monochrome

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int N = (int) 2e5 + 7;
int n;
string s;
vector<int> a;
vector<int> b;
int t[2 * N];

void clr()
{
    for (int i = 1; i <= 2 * n; i++)
    {
        t[i] = 0;
    }
}

void add(int i, int x)
{
    i++;
    while (i <= 2 * n)
    {
        t[i] += x;
        i += i & (-i);
    }
}

int sum(int i)
{
    i++;
    int sol = 0;
    while (i)
    {
        sol += t[i];
        i -= i & (-i);
    }
    return sol;
}

int sum(int i, int j)
{
    return sum(j) - sum(i - 1);
}

ll get(int k)
{
    vector<pair<int, int>> p;
    for (int i = 0; i < n; i++)
    {
        p.push_back({a[i], b[(i + k) % n]});
    }
    for (auto &it : p)
    {
        if (it.second < it.first)
        {
            swap(it.first, it.second);
        }
    }
    sort(p.begin(), p.end());
    ll sol = 0;
    clr();
    for (int i = 0; i < (int) p.size(); i++)
    {
        sol += sum(p[i].first, p[i].second);
        add(p[i].second, +1);
    }
    return sol;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);

    cin >> n >> s;
    for (int i = 0; i < 2 * n; i++)
    {
        if (s[i] == 'W')
        {
            a.push_back(i);
        }
        else
        {
            b.push_back(i);
        }
    }
    int l = 0, r = n - 2;
    ll sol = max(get(0), get(n - 1));
    while (l <= r)
    {
        int m = (l + r) / 2;
        ll x = get(m);
        ll y = get(m + 1);
        sol = max(sol, max(x, y));
        if (x < y)
        {
            l = m + 1;
        }
        else
        {
            r = m - 1;
        }
    }
    cout << sol << "\n";
}

• Subtask 1: 4 / 4
• Subtask 2: 21 / 21
• Subtask 3: 10 / 10
• Subtask 4: 65 / 65