bzoj3676: [Apio2014]回文串 回文树

Posted 2020-07-06 __560

回文树的裸题。

#include<bits/stdc++.h>
#define REP(i,a,b) for(int i=a;i<=b;i++)
#define MS0(a) memset(a,0,sizeof(a))

using namespace std;

typedef long long ll;
const int maxn=500100;
const int INF=1e9+10;

struct PalinTree
{
    int ch[maxn][26],f[maxn];
    int cnt[maxn],num[maxn],len[maxn];
    int s[maxn];
    int last,n,tot;
    int newnode(int l)
    {
        MS0(ch[tot]);
        cnt[tot]=0;
        num[tot]=0;
        len[tot]=l;
        return tot++;
    }
    void init()
    {
        tot=0;
        newnode(0);
        newnode(-1);
        last=0;n=0;
        s[n]=-1;f[0]=1;
    }
    int get_fail(int x)
    {
        while(s[n-len[x]-1]!=s[n]) x=f[x];
        return x;
    }
    void add(int c)
    {
        c-=\'a\';
        s[++n]=c;
        last=get_fail(last);
        if(!ch[last][c]){
            int cur=newnode(len[last]+2);
            f[cur]=ch[get_fail(f[last])][c];
            ch[last][c]=cur;
            num[cur]=num[f[cur]]+1;
        }
        last=ch[last][c];
        cnt[last]++;
    }
    void count()
    {
        for(int i=tot-1;i>=0;i--) cnt[f[i]]+=cnt[i];
    }
    ll work()
    {
        ll ans=0;
        REP(i,0,tot-1) ans=max(ans,1LL*len[i]*cnt[i]);
        return ans;
    }
};PalinTree pt;
char s[maxn];

int main()
{
    freopen("in.txt","r",stdin);
    while(~scanf("%s",s)){
        int len=strlen(s);
        pt.init();
        REP(i,0,len-1) pt.add(s[i]);
        pt.count();
        printf("%lld\\n",pt.work());
    }
    return 0;
}

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