[Explanations] [JSOI2013] knowledge of the game

Face questions

answer

This data range, click on the DP directly over
to see the man open a new circle or added to another circle going
attention, open a new circle requires a minimum of three people
set \ (f [i] [j ] \) for the first \ (I \) individuals \ (J \) number of turns of the program
\ [f [i] [j ] = \ begin {cases} f [i - 1] [j] * (i - 1) \\ f [ i - 3] [j - 1
] * (i - 1) * (i - 2) \\ \ end {cases} \] did not

Code

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

int n, k, mod, f[3005][3005]; 

template < typename T >
inline T read()
{
    T x = 0, w = 1; char c = getchar();
    while(c < '0' || c > '9') { if(c == '-') w = -1; c = getchar(); }
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * w; 
}

int main()
{
    n = read <int> (), k = read <int> (), mod = read <int> ();
    if(n < 3) { puts("0"); return 0; }
    f[0][0] = 1; 
    for(int i = 3; i <= n; i++)
    for(int j = 1; j <= min(i / 3, k); j++)
        f[i][j] = (1ll * (i - 1) * (i - 2) % mod * f[i - 3][j - 1] % mod + 1ll * f[i - 1][j] * (i - 1) % mod) % mod; 
    printf("%d\n", f[n][k]); 
    return 0; 
}