2020牛客多校第六场

A.African Sort

B.Binary Vector

C.Combination of Physics and Maths

D.Data structure

E.Easy Construction

F.Fibonacci Partition

G.Grid Coloring

H.Harmony Pairs

const int mod=1e9+7;
char s[102];
int dp[102][1801][2][2];
ll dfs(int n,int sum,int t,bool lim){
    if (!n)return sum>900;
    if (~dp[n][sum][t][lim])return dp[n][sum][t][lim];
    int up=lim?s[n]-'0':9;
    ll ans=0;
    for (int i=0;i<=up;i++){//B
        for (int j=0;j<=9;j++){//A
            if (t&&j>i)continue;
            (ans+=dfs(n-1,sum+j-i,t&&(i==j),lim&&(i==up)))%=mod;
        }
    }
    return dp[n][sum][t][lim]=ans;
}
int main(){
    memset(dp,-1,sizeof dp);
    scanf("%s",s+1);
    int len=strlen(s+1);
    reverse(s+1,s+1+len);
    printf("%d\n",dfs(len,900,1,1));
    return 0;
}

I.Interesting Stiriling

J.Josephus Transform

K.K-Bag