Submission #1477035

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> pip;
typedef pair<pll, pll> P;
const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS = 1e-9;
const bool debug = 0;
//---------------------------------//

ll dp[3001][3001][2];
int N, M;

int main() {
	cin >> N >> M;
	
	FOR(i, 1, N + 1) dp[0][i][0] = 1;
	dp[0][0][1] = 1;
	
	REP(i, M) {
		REP(j, N + 1) {
			REP(k, 2) {
				if (j != 0) {
					if (j == 1) {
						(dp[i + 1][j - 1][1] += dp[i][j][k]) %= MOD;
						(dp[i + 1][j][1] += dp[i][j][k]) %= MOD;
					}
					else {
						(dp[i + 1][j - 1][k] += dp[i][j][k]) %= MOD;
						(dp[i + 1][j][k] += dp[i][j][k]) %= MOD;
					}
				}
				
				if (j != N) {
					(dp[i + 1][j + 1][k] += dp[i][j][k]) %= MOD;
					(dp[i + 1][j][k] += dp[i][j][k]) %= MOD;
				}
			}
		}
	}
	
	ll ans = 0;
	REP(i, N + 1) ans += dp[M][i][1];
	ans %= MOD;
	
	cout << ans << endl;
	
	return 0;
}

Submission Info

Judge Result