F. Rhyme scheme

题： https://nanti.jisuanke.com/t/41414

#include<bits/stdc++.h>
using namespace std;
typedef __int128 ll;
const int M=;
const int mod=1e9+;
ll dp[M][M];
int a[M];
int n;
 
inline ll read() {
    ll x = , f = ;
    char c = getchar();
    for (; !isdigit(c);c = getchar()) if (c == '-') f = -;
    for (; isdigit(c); c = getchar()) x = x *  + c - '';
    return x * f;
}
ll dfs1(int pos,int up){
    if(pos==n+)
        return ;
    if(~dp[pos][up])
        return dp[pos][up];
    ll sum=;
    for(int i=;i<=up;i++){
        sum+=dfs1(pos+,max(up,i+));
    }
    dp[pos][up]=sum;
    return sum;
}
void dfs2(int pos,int up,ll r){
    if(pos==n+){
        for(int i=;i<=n;i++)
            putchar(a[i]+'A');
        puts("");
        return ;
    }
    for(int i=;i<=up;i++){
        int nowup=max(i+,up);
        if(r<=dp[pos+][nowup]){
            a[pos]=i;
            dfs2(pos+,nowup,r);
            break;
        }
        else
            r-=dp[pos+][nowup];
    }
}
int main(){
    int t;
    scanf("%d",&t);
    for(int ca=;ca<=t;ca++){
        scanf("%d",&n);
        ll k=read();
        for(int i=;i<M;i++)
            for(int j=;j<M;j++)
                dp[i][j]=-;
        for(int i=;i<M;i++)
            dp[n+][i]=;
    //    cout<<"!!"<<endl;
        dfs1(,);
        printf("Case #%d: ",ca);
        dfs2(,,k);
    }
    return ;
}