Submission #1012747

#	Time	Username	Problem	Language	Result	Execution time	Memory
1012747		snpmrnhlol	Festivals in JOI Kingdom 2 (JOI23_festival2)	C++17	100 / 100	7849 ms	1112 KiB

festival2

#include<bits/stdc++.h>
using namespace std;
const int N = 2e4;
const int NR = 2*N;
int n,mod;
int dp[N + 1][2];
int fact[NR + 1], inv[NR + 1];
int fastexp(int a,int b){
    int r = 1;
    while(b){
        if(b&1)r = 1ll*r*a%mod;
        a = 1ll*a*a%mod;
        b/=2;
    }
    return r;
}
void precalc(){
    fact[0] = 1;
    for(int i = 1;i <= NR;i++){
        fact[i] = 1ll*fact[i - 1]*i%mod;
    }
    inv[NR] = fastexp(fact[NR],mod - 2);
    for(int i = NR - 1;i >= 0;i--){
        inv[i] = 1ll*inv[i + 1]*(i + 1)%mod;
    }
}
int comb(int n, int k){
    if(n < 0 || k < 0 || k > n)return 0;
    return 1ll*fact[n]*inv[k]%mod*inv[n - k]%mod;
}
///assume all are seperate
int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin>>n>>mod;
    precalc();
    dp[2][1] = 1;
    dp[1][0] = 1;
    for(int i = 0;i <= n;i++){
        for(int j = 0;i + j <= n;j++){
            if(i >= 2 && i + j + 2 <= n){
                //cout<<i<<' '<<j<<' '<<2<<' '<<1ll*dp[i][1]*comb(j + 2,2)%mod<<' '<<1ll*inv[2*i - 3]%mod*fact[2*i - 3 + j]%mod*2%mod<<'\n';
                dp[i + j + 2][1] = (dp[i + j + 2][1] + 1ll*dp[i][1]*comb(j + 2,2)%mod*inv[2*i - 3]%mod*fact[2*i - 3 + j]%mod*2%mod)%mod;
            }
            if(i >= 1 && i + j + 2 <= n){
                dp[i + j + 2][1] = (dp[i + j + 2][1] + 1ll*dp[i][0]*(j + 1)%mod*inv[2*i - 2]%mod*fact[2*i - 2 + j]%mod)%mod;
            }
            if(i >= 1 && i + j + 1 <= n){
                dp[i + j + 1][0] = (dp[i + j + 1][0] + 1ll*dp[i][1]*(j + 1)%mod*inv[2*i - 3]%mod*fact[2*i - 3 + j]%mod)%mod;
            }
            if(i >= 1 && i + j + 1 <= n){
                dp[i + j + 1][0] = (dp[i + j + 1][0] + 1ll*dp[i][0]*inv[2*i - 2]%mod*fact[2*i - 2 + j]%mod)%mod;
            }
        }
    }
    int tot = 0;
    int all = 1;
    for(int i = 0;i <= n;i++){
        //cout<<dp[i][0]<<' '<<dp[i][1]<<' '<<1ll*dp[i][1]*(n - i + 1)%mod*fact[2*i - 3 + (n - i)]*inv[2*i - 3]%mod<<'\n';
        tot = (tot + 1ll*dp[i][1]*(n - i + 1)%mod*fact[2*i - 3 + (n - i)]%mod*inv[2*i - 3]%mod)%mod;
        tot = (tot + 1ll*dp[i][0]*fact[2*i - 2 + (n - i)]%mod*inv[2*i - 2]%mod)%mod;
        if(i)all = 1ll*all*(2*i - 1)%mod;
    }
    cout<<(all - tot + mod)%mod<<'\n';
    return 0;
}
/**
4 100000007
**/

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 27 / 27
• Subtask 4: 14 / 14
• Subtask 5: 36 / 36
• Subtask 6: 13 / 13