模板--后缀自动机

• 你没有看错，菜鸡退役前刚学后缀自动机

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<queue>
#define ll long long 
#define M 2000010
#define mmp make_pair
using namespace std;
int read()
{
	int nm = 0, f = 1;
	char c = getchar();
	for(; !isdigit(c); c = getchar()) if(c == '-') f = -1;
	for(; isdigit(c); c = getchar()) nm = nm * 10 + c - '0';
	return nm * f;
}
int fa[M], ch[M][26], len[M], sz[M], t[M], a[M], lst = 1, cnt = 1;
char s[M];

void insert(int c)
{
	int f = lst, p = ++cnt;
	lst = p;
	len[p] = len[f] + 1;
	sz[p] = 1;
	while(f && !ch[f][c]) ch[f][c] = p, f = fa[f];
	if(!f)
	{
		fa[p] = 1;
		return;
		//情况1 
	}
	int q = ch[f][c], nq = ++cnt;
	if(len[f] + 1 == len[q])
	{
		fa[p] = q;
		cnt--;
		//情况二 max = min - 1 
		return;
	}
	// 情况3 有中转 
	len[nq] = len[f] + 1;
	fa[nq] = fa[q];
	fa[q] = fa[p] = nq;
	memcpy(ch[nq], ch[q], sizeof(ch[nq]));
	while(f && ch[f][c] == q) ch[f][c] = nq, f = fa[f];
}

int main()
{
	scanf("%s", s + 1);
	int le = strlen(s + 1);
	for(int i = 1; i <= le; i++) insert(s[i] - 'a');
	for(int i = 1; i <= cnt; i++) t[len[i]]++;
	for(int i = 1; i <= cnt; i++) t[i] += t[i - 1];
	for(int i = 1; i <= cnt; i++) a[t[len[i]]--] = i;
	ll ans = 0; 
	for(int i = cnt; i >= 1; i--)
	{
		int now = a[i];
		sz[fa[now]] += sz[now];
		if(sz[now] > 1) ans = max(ans, 1ll * sz[now] * len[now]);
	}
	cout << ans << "\n";
	return 0;
}