Submission #649214

#	Time	Username	Problem	Language	Result	Execution time	Memory
649214		boris_mihov	NoM (RMI21_nom)	C++17	100 / 100	260 ms	71028 KiB

Main

#include <unordered_map>
#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>
#include <set>

typedef long long llong;
const int MAXN = 2000 + 10;
const int MOD  = 1e9 + 7;
const int INF  = 1e9;

int n, m;
int fact[MAXN];
int var[MAXN][MAXN];
int comb[MAXN][MAXN];
inline llong getKey(int idx, int zeros, int ones)
{
    return 1LL * idx * MAXN * MAXN + zeros * MAXN + ones;
}

std::unordered_map <llong,int> dp;
int f(int idx, int zeros, int ones)
{
    if (idx == 0)
    {
        return (zeros == 0 && ones == 0);
    }

    llong key = getKey(idx, zeros, ones);
    if (dp.count(key))
    {
        return dp[key];
    }

    int res = 0;
    int len = (2*n - idx + 1) / m + (idx != 1);
    for (int addOnes = std::max(0, len - ones) ; addOnes <= std::min(len, zeros) ; ++addOnes)
    {
        res += (((((1LL * f(idx-1, zeros - addOnes, ones + 2*addOnes - len) * comb[len][addOnes]) % MOD) * var[zeros][addOnes]) % MOD) * var[ones][len - addOnes]) % MOD;
        if (res >= MOD) res -= MOD;
    }

    return dp[key] = res;
}
void solve()
{
    for (int i = 0 ; i <= n ; ++i)
    {
        comb[i][0] = 1;
    }

    fact[0] = 1;
    for (int i = 1 ; i <= n ; ++i)
    {
        fact[i] = (1LL * fact[i-1] * i) % MOD;
    }

    for (int i = 1 ; i <= n ; ++i)
    {
        for (int j = 1 ; j <= i ; ++j)
        {
            comb[i][j] = comb[i-1][j] + comb[i-1][j-1];
            if (comb[i][j] >= MOD) comb[i][j] -= MOD;
        }
    }

    for (int i = 0 ; i <= n ; ++i)
    {
        for (int j = 0 ; j <= i ; ++j)
        {
            var[i][j] = (1LL * comb[i][j] * fact[j]) % MOD; 
        }
    }

    int ans = f(m, n, 0);
    for (int i = 1 ; i <= n ; ++i)
    {
        ans *= 2;
        ans %= MOD;
    }

    std::cout << ans << '\n';
}

void read() 
{
    std::cin >> n >> m;
}

void fastIO()
{
    std::ios_base :: sync_with_stdio(0);
    std::cout.tie(nullptr);
    std::cin.tie(nullptr);
}

int main()
{
    fastIO();
    read();
    solve();

    return 0;
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 18 / 18
• Subtask 5: 48 / 48