[BZOJ3676][APIO2014]回文串(Manacher+SAM)

#include
#include
#include
#define rep(i,l,r) for (int i=l; i
typedef long long ll;
using namespace std;

const int N=600100;
int cnt=1,lst=1,n,tot[N],mx[N],p[N],pos[N],son[N][27],fa[N],f[N][20],q[N],R[N];
ll ans; char s[N],S[N];

void ext(int c,int x){
    int p=lst,np=lst=++cnt; mx[np]=mx[p]+1; R[np]=1; pos[x]=np;
    while (!son[p][c] && p) son[p][c]=np,p=fa[p];
    if (!p) fa[np]=1;
    else{
        int q=son[p][c];
        if (mx[q]==mx[p]+1) fa[np]=q;
        else{
            int nq=++cnt; mx[nq]=mx[p]+1;
            memcpy(son[nq],son[q],sizeof(son[q]));
            fa[nq]=fa[q]; fa[q]=fa[np]=nq;
            while (son[p][c]==q && p) son[p][c]=nq,p=fa[p];
        }
    }
}

void pre(){
    rep(i,1,cnt) tot[mx[i]]++;
    rep(i,1,n) tot[i]+=tot[i-1];
    for (int i=cnt; i; i--) q[tot[mx[i]]--]=i;
    for (int i=cnt; i; i--) R[fa[q[i]]]+=R[q[i]];
    rep(i,1,cnt){
        f[i][0]=fa[i];
        rep(j,1,19) f[i][j]=f[f[i][j-1]][j-1];
    }
}

void get(int l,int r){
    l=(l>>1)+(l&1); r>>=1; int x=pos[r];
    for (int i=19; ~i; i--)
        if (mx[f[x][i]]>=r-l+1) x=f[x][i];
    ans=max(ans,1ll*R[x]*(r-l+1));
}

void manacher(){
    int mxlen=0,id;
    rep(i,1,n){
        if (mxlen>i) p[i]=min(mxlen-i,p[2*id-i]);
            else{ p[i]=1; if (S[i]!=‘#‘) get(i,i); }
        while (S[i+p[i]]==S[i-p[i]]) get(i-p[i],i+p[i]),p[i]++;
        if (p[i]+i>mxlen) mxlen=p[i]+i,id=i;
    }
}

int main(){
    freopen("palindromes.in","r",stdin);
    freopen("palindromes.out","w",stdout);
    scanf("%s",s+1); n=strlen(s+1);
    rep(i,1,n) ext(s[i]-‘a‘,i);
    pre(); S[0]=‘$‘; S[1]=‘#‘;
    rep(i,1,n) S[(i1)+1]=‘#‘,S[i1]=s[i];
    n=(n1)+1; manacher(); printf("%lld\n",ans);
    return 0;
}