CSES-Dynamic-Programming/Array Description at main · UKS28/CSES-Dynamic-Programming · GitHub

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#include <bits/stdc++.h>
using namespace std;
#define rep(k,z) for(int i=k;i<z;i++)
#define ll  long long int
int MOD=1e9+7;

// https://www.youtube.com/watch?v=PLpzng35N54

int main()
{
    ll n,m;
    cin>>n>>m;
    vector<ll> v(n);
    rep(0,n)
    cin>>v[i];
    vector<vector<ll>> dp(n,vector<ll>(m+1,0));

    // dp[i][j]---> number of desired array with ith index as j.


    if(v[0]!=0)
    {
       dp[0][v[0]]=1;
    }

    else
    {

        for(int i=1;i<=m;i++)
            dp[0][i]=1;
    }

    for(int i=1;i<n;i++)
    {
      if(v[i]==0)
      {
         for(int j=1;j<=m;j++)
         {
            if(j-1>0)
             (dp[i][j]+=dp[i-1][j-1])%=MOD;
            (dp[i][j]+=dp[i-1][j])%=MOD;
            if(j+1<=m)
            (dp[i][j]+=dp[i-1][j+1])%=MOD;
         }
      }
      else
      {
        if(v[i]-1>0)
          (dp[i][v[i]]+=dp[i-1][v[i]-1])%=MOD;
         (dp[i][v[i]]+=dp[i-1][v[i]])%=MOD;
        if(v[i]+1<=m)
        (dp[i][v[i]]+=dp[i-1][v[i]+1])%=MOD;
      }
    }
    ll sum=0;
    if(v[n-1]==0)
    for(int i=1;i<=m;i++)
       (sum+=dp[n-1][i])%=MOD;
    else
    sum+=dp[n-1][v[n-1]];

    cout<<sum<<endl;

}