Submission #1481427

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back((a))
#define all(x) (x).begin(),(x).end()
#define uniq(x) sort(all(x)),(x).erase(unique(all(x)),end(x))
#define fi first
#define se second
#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
void _dbg(string){cout<<endl;}
template<class H,class... T> void _dbg(string s,H h,T... t){int l=s.find(',');cout<<s.substr(0,l)<<" = "<<h<<", ";_dbg(s.substr(l+1),t...);}
template<class T,class U> ostream& operator<<(ostream& o, const pair<T,U> &p){o<<"("<<p.fi<<","<<p.se<<")";return o;}
template<class T> ostream& operator<<(ostream& o, const vector<T> &v){o<<"[";for(T t:v){o<<t<<",";}o<<"]";return o;}

#define INF 1120000000
#define MOD 1000000007

const int X = 3005;
long dp[2][X+5][2];

int main(){
  int n,m;
  cin>>n>>m;

  auto prev = dp[0];
  auto nxt = dp[1];

  fill(prev[0], prev[X+1], 0L);
  repl(i,1,n+1) prev[i][0] = 1;
  prev[0][1] = 1;

  rep(i,m){
    // [j] blue j, red N-j, [k] visited j==0
    fill(nxt[0], nxt[X+1], 0);
    rep(j,n+1)rep(k,2) if(prev[j][k]>0){
      if(j>0){
        nxt[j][k|(j==1)] += prev[j][k]; // b r
        nxt[j-1][k|(j==1)] += prev[j][k]; // b b
      }
      if(j<n){
        nxt[j][k] += prev[j][k]; // r b
        nxt[j+1][k] += prev[j][k]; // r b
      }
    }
    rep(j, n)rep(k,2) nxt[j][k] %= MOD;
    swap(nxt, prev);
  }

  long ans = 0;
  rep(i,n+1) ans += prev[i][1];

  cout << ans%MOD << endl;

  return 0;
}

Submission Info

Judge Result