Submission #767426

#	Time	Username	Problem	Language	Result	Execution time	Memory
767426		PurpleCrayon	Chorus (JOI23_chorus)	C++17	40 / 100	7044 ms	468 KiB

chorus

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

#define sz(v) int(v.size())
#define ar array
typedef long long ll;
const int N = 5e3+10, MOD = 1e9+7;

int n, K, small[N];
int ps[N], l_use[N];
vector<int> one, two;

void solve() {
    cin >> n >> K;
    for (int i = 0; i < 2 * n; i++) {
        char c; cin >> c;
        if (c == 'A') one.push_back(i);
        else two.push_back(i);
    }

    // for (int x : one) cerr << x << ' '; cerr << endl;
    // for (int x : two) cerr << x << ' '; cerr << endl;

    for (int i = 0; i < n; i++) {
        small[i] = lower_bound(two.begin(), two.end(), one[i]) - two.begin();
    }

    for (int i = 0; i < n; i++) {
        ps[i] = small[i] + (i ? ps[i-1] : 0);
        l_use[i] = -(i ? ps[i-1] : 0);
        for (int j = i; j < n; j++) {
            if (small[j] < i) {
                l_use[i] -= small[j] - i;
            }
        }
    }

    auto COST = [&](int l, int r) {
        return ps[r] + l_use[l] - l * (r - l + 1);
    };

    /*
    for (int l = 0; l < n; l++) {
        int cur = 0;
        for (int r = l; r < n; r++) {
            cur += max(small[r] - l, 0);
            cost[l][r] = cur;
        }
    }
    

    for (int i = 0; i < n; i++) {
        for (int j = i; j < n; j++) {
            int one = cost[i][j];
            int two = COST(i, j);
            assert(one == 0 && two > 0 || one == two);
        }
    }
    */

    vector<int> prv(n, MOD);
    for (int k = 1; k <= K; k++) {
        vector<int> nxt(n, MOD);
        for (int i = 0; i < n; i++) {
            for (int l = i; l >= 0; l--) {
                nxt[i] = min(nxt[i], COST(l, i) + (l == 0 ? 0 : prv[l-1]));
            }

            int l = small[i];
            if (l <= i) {
                nxt[i] = min(nxt[i], (l == 0 ? 0 : prv[l-1]));
            }
        }
        swap(prv, nxt);
    }

    cout << prv[n-1] << '\n';
}

int main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int T = 1;
    // cin >> T;
    while (T--) solve();
}

• Subtask 1: 16 / 16
• Subtask 2: 24 / 24
• Subtask 3: 0 / 21
• Subtask 4: 0 / 26
• Subtask 5: 0 / 13