浅谈 Manacher

#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 LL 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=1e5+10;
char s[N<<1],str[N];
LL pre[N<<1],suf[N<<1],sum[N<<1];
int len,p[N<<2],L;
I void init(){
    RI i;for(s[0]='$',s[1]='#',L=2,i=0;i<len;i++) s[L++]=str[i],s[L++]='#';s[L]='\0';
}
I void Manacher(){
    RI mx=0,id=0,i;for(init(),i=1;i<L;i++){
        if(i<mx) p[i]=min(p[2*id-i],mx-i);
        else p[i]=1;
//        p[i]=min(mx-i,p[id*2-i]);
        W(s[i-p[i]]==s[i+p[i]]) p[i]++;
        if(mx<i+p[i]) id=i,mx=i+p[i];
    }
}
int main(){
    RI i;W(~scanf("%s",&str)){
        len=strlen(str);for(i=0;i<=len;i++) suf[i]=pre[i]=sum[i]=0;
        for(Manacher(),i=2;i<=len*2;i++) suf[(i+1)/2]++,suf[(i+1)/2+p[i]/2]--;
        for(i=len*2;i>=2;i--) pre[i/2]++,pre[i/2-p[i]/2]--;
        for(i=len;i>=1;i--) pre[i]+=pre[i+1];
        for(i=1;i<=len;i++) suf[i]+=suf[i-1],sum[i]=sum[i-1]+suf[i];
        LL Ans=0;for(i=1;i<=len;i++) Ans+=(LL)pre[i]*sum[i-1];
        writeln(Ans);
    }return 0;
}