Solution: When I write know why. Anyway, I think the question is a palindrome automaton difficult.
#include<bits/stdc++.h> #define ls (x<<1) #define rs (x<<1|1) #define ll long long #define pb push_back #define mp make_pair #define db double #define pii pair<int,int> using namespace std; const int M=1e4+7; const int N=1e6+7; const int inf=1e9; inline ll read() { ll x=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} return x*f; } int T; char S[N]; ll aa[N]; int n,base,mod; int a [N] [26], with [N] fail [N], half [N], pq [N]; Pam struct { int last,tot; ll cnt[N],val[N]; ll ans; int vis[N]; ll tmp; void init(){ for(int i=0;i<=tot;i++){ cnt[i]=len[i]=0; } for(int i=0;i<=tot;i++)for(int j=0;j<26;j++)son[i][j]=0; len[1]=-1;tot=1;last=0;fail[0]=fail[1]=1; ans=0;tmp=0; } void extend(int c,int pl,char *S){ int p=last;int q,r; while(S[pl-len[p]-1]!=S[pl]){p=fail[p];} if(!son[p][c]){ q=++tot,r=fail[p]; len[q]=len[p]+2; while(S[pl-len[r]-1]!=S[pl])r=fail[r]; fail[q]=son[r][c]; son[p][c]=q; } last=son[p][c]; cnt[last]++; } void cal(){ if(x>1&&view [x]) tmp = (TMP-cnt [x] * AA [n-len [x]]% v)% against, vis [x] = 0; while(T--){ cin>>n>>base>>mod; scanf("%s",S+1); aa[0]=1; int len=strlen(S+1); for(int i=1;i<=n;i++)aa[i]=aa[i-1]*base%mod; //for(int i=1;i<=n;i++)cout<<aa[i]<<" ";cout<<"\n"; pam.init(); for(int i=1;i<=len;i++){ pam.extend(S[i]-'a',i,S); } pam.cal(); pam.dfs(0); //cout<<pam.tmp<<"\n"; pam.dfs(1); //cout<<pam.cnt[0]<<pam.cnt[1]<<"\n"; cout<<"Case "<<++cas<<": "<<(pam.ans%mod+mod)%mod<<"\n"; } }