Submission #6508583

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Source Code Expand

#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#define MOD 1000000007
#define mkp make_pair
typedef long long ll;
using namespace std;

#define MAX_N 200020
ll inv[MAX_N+10],fac[MAX_N+10],ifac[MAX_N+10];

void setComb(){
  inv[0]=1;inv[1]=1;fac[1]=1;ifac[1]=1;fac[0]=1;ifac[0]=1;
  for(int i=2;i<MAX_N;i++){
    inv[i]=(-MOD/i)*inv[MOD%i]%MOD;
    fac[i]=fac[i-1]*i%MOD;
    ifac[i]=ifac[i-1]*inv[i]%MOD;
  }
  return;
}

ll comb(ll n,ll k){
  if(n<k||n<0||k<0) return 0;
  else return ((fac[n]*ifac[k]%MOD*ifac[n-k]%MOD+MOD)%MOD);
}

ll hcomb(ll n,ll r){
  if(n==0&&r==0) return 1;
  else if(n<0||r<0) return 0;
  else return comb(n+r-1,r-1);
}

int main(){
  int N;
  cin>>N;
  vector<ll> A(N);
  for(int i=0;i<N;i++) cin>>A[i];

  vector<pair<int,ll>> v;
  int len=0,val=0;
  for(int i=0;i<N;i++){
      if(A[i]!=-1){
          if(len==0) continue;
          v.push_back(mkp(len+1,A[i]-val));
          len=0;
          val=0;
      }else{
          if(len==0) val=A[i-1];
          len++;
      }
  }
  setComb();

  ll ans=1;
  for(int i=0;i<v.size();i++){
      ll a,b;
      tie(a,b)=v[i];

      ll n=a+b-1;
      b=min(b,n-b);

      ll res=1;
      for(ll j=0;j<b;j++){
          ll z=(n-j)%MOD;
          res=res*z%MOD;
      }
      for(int j=1;j<=b;j++){
          ll z=inv[j]%MOD;
          res=res*z%MOD;
      }
      ans=ans*res%MOD;
  }

  cout<<(ans+MOD)%MOD<<endl;

  return 0;
}

Submission Info

Judge Result