【DP】 ACdream 1412 2-3 Trees

#include <iostream>  
#include <queue>  
#include <stack>  
#include <map>  
#include <set>  
#include <bitset>  
#include <cstdio>  
#include <algorithm>  
#include <cstring>  
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn  10005
#define maxm 300005
#define eps 1e-10
//#define mod 1315423911
#define INF 1e17
#define lowbit(x) (x&(-x))
#define mp make_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R  
typedef long long LL;
typedef unsigned long long ULL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
//LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='
')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
// head

LL dp[maxn << 2];
LL c[2][maxn];
int n, mod;

void init(void)
{
	memset(dp, 0, sizeof dp);
	memset(c, 0, sizeof c);
}

void work(void)
{
	int now = 0;
	dp[1] = 1;
	c[0][0] = c[0][1] = 1;
	for(int i = 1; i <= n; i++) {
		for(int j = 0; j <= i; j++) {
			int t1 = j*2, t2 = (i - j) * 3;
			dp[t1 + t2] = (dp[t1 + t2] + c[now][j] * dp[i]) % mod;
		}
		for(int j = 1; j <= i; j++) c[now^1][j] = (c[now][j] + c[now][j-1]) % mod;
		c[now^1][0] = c[now^1][i+1] = 1;
		now = now^1;
	}
	printf("%lld
", dp[n]);
}

int main(void)
{
	while(scanf("%d%d", &n, &mod)!=EOF) {
		init();
		work();
	}
	return 0;
}