义乌中学暑假集训 2021.07.13 B

#include<bits/stdc++.h>
#define Tp template<typename Ty>
#define Ts template<typename Ty,typename... Ar>
#define W while
#define I inline
#define RI register int
#define int long long
#define Cn const
#define CI Cn int&
#define gc getchar
#define D isdigit(c=gc())
#define pc(c) putchar((c))
#define min(x,y) ((x)<(y)?(x):(y))
#define max(x,y) ((x)>(y)?(x):(y))
using namespace std;
namespace Debug{
    Tp I void _debug(Cn char* f,Ty t){cerr<<f<<'='<<t<<endl;}
    Ts I void _debug(Cn char* f,Ty x,Ar... y){W(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
    Tp ostream& operator<<(ostream& os,Cn vector<Ty>& V){os<<"[";for(Cn auto& vv:V) os<<vv<<",";os<<"]";return os;}
    #define gdb(...) _debug(#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
namespace FastIO{
    Tp I void read(Ty& x){char c;int f=1;x=0;W(!D) f=c^'-'?1:-1;W(x=(x<<3)+(x<<1)+(c&15),D);x*=f;}
    Ts I void read(Ty& x,Ar&... y){read(x),read(y...);}
    Tp I void write(Ty x){x<0&&(pc('-'),x=-x,0),x<10?(pc(x+'0'),0):(write(x/10),pc(x%10+'0'),0);}
    Tp I void writeln(Cn Ty& x){write(x),pc('\n');}
}using namespace FastIO;
Cn int N=1e6+10,P=998244353;
int n,Ans,a[N],F[5][64][64],Sum,sm[64],SS;
char b[N];
signed main(){
    RI i,j,k,t,l,e;cin>>b+1;n=strlen(b+1);for(i=1;i<=n;i++) a[i]=('a'<=b[i]&&b[i]<='z')?(b[i]-'a'):(('A'<=b[i]&&b[i]<='Z')?(b[i]-'A'+26):(b[i]-'0'+52));
    for(i=1;i<=n;i++) Sum++,SS+=sm[a[i]]++;for(i=n;i>=1;i--){
        Sum--,SS-=--sm[a[i]];
        for(j=0;j<=61;j++) if(a[i]^j){
            F[1][a[i]][j]++;
            (F[3][j][a[i]]+=F[2][j][a[i]])%=P;
            (F[2][a[i]][j]+=F[1][j][a[i]])%=P;
            (Ans+=F[3][a[i]][j]*((Sum-sm[a[i]]-sm[j])*((Sum-sm[a[i]]-sm[j])-1)/2%P-SS+(sm[a[i]]*(sm[a[i]]-1)/2)%P+(sm[j]*(sm[j]-1)/2)%P)%P)%=P;
        }
    }
    return write(Ans),0;
}