AC自动机的fail可以成树 KMP的next也能成树

这道题就是沿着树往上统计出现次数

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cstring>
using namespace std;

const int N=100005;

int n; char S[N];
int next[N];
int cnt[N];

int main(){
  scanf("%s",S+1); n=strlen(S+1);
  int k=0;
  for (int i=2;i<=n;i++){
    while (k && S[k+1]!=S[i]) k=next[k];
    if (S[k+1]==S[i]) k++;
    next[i]=k;
    cnt[k]++;
  }
  long long ans=0;
  for (int i=n;i;i--){
    ans=max(ans,(long long)i*(cnt[i]+1));
    cnt[next[i]]+=cnt[i];
  }
  printf("%lld\n",ans);
  return 0;
}