Submission #1161323

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Source Code Expand

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

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define mp(a,b) make_pair(a,b)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;

#define INF INT_MAX/3

#define MAX_N 100

#define m 1000000007

int n;
ll a[2020];

ll mod_pow(ll a,ll n,ll mod){
  ll res=1;
  while(n>0){
    if(n&1)res=res*a%mod;
    a=a*a%mod;
    n>>=1;
  }
  return res;
}

ll calc_comb(ll n,ll k,ll mod){
  ll res=1;
  repl(i,1,k+1){
    res=res*(n-i+1)%mod;
    res=res*mod_pow(i,mod-2,mod)%mod;
  }
  return res;
}

int main(){
	cin.sync_with_stdio(false);
  ll res=1;
  cin>>n;
  rep(i,n)cin>>a[i];
  for(int i=0;i<n;){
    int j=i+1;
    if(j==n)break;
    while(j<n&&a[j]==-1)j++;
    res=res*calc_comb(a[j]-a[i]+1+j-i-2,j-i-1,m)%m;
    i=j;
  }
  cout<<res<<endl;
	return 0;
}

Submission Info

Judge Result