Submission #228373

#	Time	Username	Problem	Language	Result	Execution time	Memory
228373		FieryPhoenix	Linear Garden (IOI08_linear_garden)	C++11	90 / 100	216 ms	65536 KiB

linear_garden

#include <bits/stdc++.h>
using namespace std;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef long long ll;
typedef long double ld;
#define INF 2001001001
#define MOD 1000000007

int N,M;
string S;
int dp[1000001][3][3][2];//index, max(L-P), max(P-L), 0 for L

int main()
{
  //ios_base::sync_with_stdio(0);cin.tie(0);
  //freopen (".in","r",stdin);
  //freopen (".out","w",stdout);
  cin>>N>>M;
  cin>>S;
  dp[N][0][0][0]=1;
  for (int i=N-1;i>=0;i--){
    //adding L
    for (int j=0;j<2;j++)
      for (int k=0;k<=2;k++)
	for (int l=0;l<2;l++){
	  dp[i][j+1][max(0,k-1)][0]+=dp[i+1][j][k][l];
	  dp[i][j+1][max(0,k-1)][0]%=M;
	}
    //adding P
    for (int j=0;j<=2;j++)
      for (int k=0;k<2;k++)
	for (int l=0;l<2;l++){
	  dp[i][max(0,j-1)][k+1][1]+=dp[i+1][j][k][l];
	  dp[i][max(0,j-1)][k+1][1]%=M;
	}
  }
  int L_P=0,P_L=0;
  int ans=0;
  for (int i=0;i<N;i++){
    //cout<<"I: "<<i<<endl;
    if (S[i]=='P'){
      for (int j=0;j<=2;j++)
	for (int k=0;k<=2;k++)
	  if (j+L_P<=2 && k+P_L<=2){
	    ans+=dp[i][j][k][0];
	    //cout<<"add "<<dp[i][j][k][0]<<endl;
	    ans%=M;
	  }
    }
    if (S[i]=='L'){
      L_P++;
      P_L=max(0,P_L-1);
    }
    else{
      P_L++;
      L_P=max(0,L_P-1);
    }
  }
  cout<<ans+1<<endl;
  return 0;
}

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