Submission #140080

#	Time	Username	Problem	Language	Result	Execution time	Memory
140080		mlyean00	Growing Vegetable is Fun 3 (JOI19_ho_t3)	C++17	20 / 100	50 ms	508 KiB

joi2019_ho_t3

#include <bits/stdc++.h>
#ifdef DEBUG
#include "debug.hpp"
#else
#pragma GCC optimize("Ofast")
#define trace(...)
#include <bits/stdc++.h>
#define endl '\n'
#endif

using namespace std;

const string COL = "RGY";

int count_inversions(vector<int>& v, int l, int r) {
    if (r - l == 1) return 0;

    int mid = (l + r) / 2;

    int ans = 0;
    ans += count_inversions(v, l, mid);
    ans += count_inversions(v, mid, r);

    vector<int> m;
    m.reserve(r - l);
    int ptr1 = l, ptr2 = mid;

    while (ptr1 < mid || ptr2 < r) {
        if (ptr1 == mid) {
            m.push_back(v[ptr2++]);
        } else if (ptr2 == r) {
            m.push_back(v[ptr1++]);
            ans += ptr2 - mid;
        } else if (v[ptr1] < v[ptr2]) {
            m.push_back(v[ptr1++]);
            ans += ptr2 - mid;
        } else {
            m.push_back(v[ptr2++]);
        }
    }

    copy(m.begin(), m.end(), v.begin() + l);

    return ans;
}

int count_swaps(string s, string const& t) {
    int n = s.length();
    vector<stack<int>> st(3);
    for (int i = n - 1; i >= 0; --i) {
        st[COL.find(t[i])].push(i);
    }
    vector<int> v(n);
    for (int i = 0; i < n; ++i) {
        int c = COL.find(s[i]);
        if (st[c].empty()) return INT_MAX;
        v[i] = st[c].top();
        st[c].pop();
    }
    return count_inversions(v, 0, n);
}

int subtask_1(int n, string s) {
    int ans = INT_MAX;

    for (int i = 0; i < 3; ++i) {
        for (int j = 0; j < 1 << (n - 1); ++j) {
            string t;
            int prev_c = i;
            t.push_back(COL[prev_c]);
            for (int k = 0; k < n - 1; ++k) {
                int bit = (j >> k) & 1;
                prev_c = (prev_c + bit + 1) % 3;
                t.push_back(COL[prev_c]);
            }
            ans = min(count_swaps(s, t), ans);
        }
    }

    if (ans == INT_MAX) ans = -1;

    return ans;
}

int subtask_3(int n, string s) {
    string t1, t2;
    for (int i = 0; i < n; ++i) {
        t1.push_back("RG"[i % 2]);
        t2.push_back("GR"[i % 2]);
    }
    int ans = min(count_swaps(s, t1), count_swaps(s, t2));

    if (ans == INT_MAX) ans = -1;

    return ans;
}

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

    int n;
    string s;
    cin >> n >> s;

    int ans;
    if (n <= 15) {
        ans = subtask_1(n, s);
    } else {
        ans = subtask_3(n, s);
    }

    cout << ans << endl;

    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 0 / 55
• Subtask 3: 15 / 15
• Subtask 4: 0 / 25