Submission #558365

#	Time	Username	Problem	Language	Result	Execution time	Memory
558365		Yazan_Alattar	Ljetopica (COI19_ljetopica)	C++14	0 / 100	14 ms	8520 KiB

ljetopica

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define F first
#define S second
#define pb push_back
#define endl "\n"
#define aint(x) x.begin(), x.end()
const int M = 3007;
const ll inf = 2e9;
const ll mod = 1e9 + 7;
const double pi = acos(-1);
const double eps = 1e-6;
const int dx[] = {0, -1, 0, 1}, dy[] = {1, 0, -1, 0};
const int block = 320;

ll n, k, p[M], ans, c[M][M];
string s, a, b;

int main(){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin >> n >> k >> s >> a >> b;
    s = '#' + s;
    s = '#' + s;

    p[0] = 1;
    for(int i = 1; i <= n; ++i) p[i] = (p[i - 1] * 2) % mod;

    for(int i = 0; i <= n; ++i){
        c[i][0] = 1;
        for(int j = 1; j <= i; ++j) c[i][j] = (c[i - 1][j] + c[i - 1][j - 1]) % mod;
    }

    ll ans = (p[n] * c[n][k]) % mod;
    for(int i = 2; i <= n; ++i){
        for(int j = 0; j <= k; ++j){

            if(s[i] == 'L' && j && j <= i - 1 && k - j <= n - i + 1){
                ll add = (p[n - i] * c[n - i + 1][k - j]) % mod;
                add = (add * c[i - 2][j - 1]) % mod;
                ans = (ans + add) % mod;
//                cout << i << " " << j << " " << add << endl;
            }

            else if(s[i] == 'R' && j <= i - 2 && k - j <= n - i + 1){
                ll add = (p[n - i] * c[n - i + 1][k - j]) % mod;
                add = (add * c[i - 2][j]) % mod;
                ans = (ans + add) % mod;
//                cout << i << " " << j << " " << add << endl;
            }
        }
    }

    for(int i = 2; i <= n; ++i){
        if(s[i] == 'L') s[i] = 'R';
        else s[i] = 'L';
    }

    for(int i = 2; i <= n; ++i){
        for(int j = 0; j <= k; ++j){

            if(s[i] == 'L' && j && j <= i - 1 && k - j <= n - i + 1){
                ll add = (p[n - i] * c[n - i + 1][k - j]) % mod;
                add = (add * c[i - 2][j - 1]) % mod;
                ans = (ans + add) % mod;
//                cout << i << " " << j << " " << add << endl;
            }

            else if(s[i] == 'R' && j <= i - 2 && k - j <= n - i + 1){
                ll add = (p[n - i] * c[n - i + 1][k - j]) % mod;
                add = (add * c[i - 2][j]) % mod;
                ans = (ans + add) % mod;
//                cout << i << " " << j << " " << add << endl;
            }
        }
    }

    cout << ans << endl;
    return 0;
}

• Subtask 1: 0 / 8
• Subtask 2: 0 / 14
• Subtask 3: 0 / 17
• Subtask 4: 0 / 61