Add / delete

    int H,U,u,S,G;
    void add(int w,bool x){
        ++S;
        G+=(c==d)&&s[w]==c;
        if(x){
            if(s[w]==d)H+=U,H%=MOD,u+=P[S-1],u%=MOD;
            U=U*2%MOD;
            if(s[w]==c)++U;
        }else{
            if(s[w]==c)H+=u,H%=MOD,U+=P[S-1],U%=MOD;
            u=u*2%MOD;
            if(s[w]==d)++u;
        }
    }
    void del(int w,bool x){
        --S;
        G-=(c==d)&&s[w]==c;
        if(x){
            if(s[w]==c)U=(U+MOD-1)%MOD;
            U=U*IV%MOD;
            if(s[w]==d)H=H-U+MOD,H%=MOD,u+=MOD-P[S],u%=MOD;
        }else{
            if(s[w]==d)u=(u+MOD-1)%MOD;
            u=u*IV%MOD;
            if(s[w]==c)H=(H-u+MOD)%MOD,U+=MOD-P[S],U%=MOD;
        }
    }