CSES – Array Description

#include<bits/stdc++.h>
#define int long long
#define fastio ios_base::sync_with_stdio(0);cin.tie(0)
using namespace std;
//declare
const int maxn = 1e5+5, mod = 1e9+7;
int n,m;
int dp[maxn][105];
vector<int> v;
//
int solve(int i,int x){
    if(x <= 0 || x > m) return 0;
    if(v[i] && v[i] != x) return 0;
    if(i == n) return 1;
    if(dp[i][x] != -1) return dp[i][x];
    return dp[i][x] = (solve(i+1,x-1)+solve(i+1,x)+solve(i+1,x+1)) % mod;
}
signed main(){
    fastio;
    cin>>n>>m;
    v.push_back(0);
    for(int i=0;i<n;i++){
        int x; cin>>x;
        v.push_back(x);
    }
    memset(dp,-1,sizeof(dp));
    int ans = 0;
    for(int i=1;i<=m;i++){
        ans = (ans + solve(1,i)) % mod;
    }
    cout<<ans<<"\n";
    return 0;
}