Luogu3804 【模板】后缀自动机（后缀自动机）

　　建出parent树统计即可。开始memcpy处写的是sizeof(son[y])，然后就T掉了……还是少用这种东西吧。

　　同时也有SA做法。答案子串一定是名次数组中相邻两个串的lcp。单调栈统计其是几个后缀的前缀即可。

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=0,f=1;char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
    while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
#define N 2000010
int n,cnt,last,son[N][26],fail[N],size[N],len[N],t=0,p[N];
struct data{int to,nxt;
}edge[N];
void ins(int c) 
{
    int x=++cnt,p=last;last=x;len[x]=n;size[x]=1;
    while (!son[p][c]&&p) son[p][c]=x,p=fail[p];
    if (!p) fail[x]=1;
    else
    {
        int q=son[p][c];
        if (len[q]==len[p]+1) fail[x]=q;
        else
        {
            int y=++cnt;
            len[y]=len[p]+1;
            memcpy(son[y],son[q],sizeof(son[q]));
            fail[y]=fail[q],fail[x]=fail[q]=y;
            while (son[p][c]==q) son[p][c]=y,p=fail[p];
        }
    }
}
void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}
void dfs(int k)
{
    for (int i=p[k];i;i=edge[i].nxt) 
    {
        dfs(edge[i].to);
        size[k]+=size[edge[i].to];
    }
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("suffixautomaton.in","r",stdin);
    freopen("suffixautomaton.out","w",stdout);
    const char LL[]="%I64d
";
#else
    const char LL[]="%lld
";
#endif
    last=cnt=1;
    char c=getchar();
    while (c>='a'&&c<='z') n++,ins(c-97),c=getchar();
    for (int i=2;i<=cnt;i++) addedge(fail[i],i);
    dfs(1);
    long long ans=0;
    for (int i=1;i<=cnt;i++)
    if (size[i]>1) ans=max(ans,1ll*size[i]*len[i]);
    cout<<ans;
    return 0;
}