以 luogu P3804 为例
感觉我对 SAM 理解的不是很透彻。
#include <cstdio>
#include <cstring>
#define R register
#define Null b
#define Max(_A, _B) (_A > _B ? _A : _B)
char s[1000010];
struct Data
{
int len, size, In;
Data *ch[26], *pre;
} b[2000010], *last = b, *Q[2000010], **head = Q, **tail = Q;
int tot;
void Add(R int s)
{
R Data *cur = b + ++tot, *p = last, *q;
cur->len = last->len + 1;
while(p && !p->ch[s]) p->ch[s] = cur, p = p->pre;
if(p == 0) cur->pre = Null;
else
{
q = p->ch[s];
if(q->len == p->len + 1) cur->pre = q;
else
{
R Data *clone = b + ++tot; *clone = *q;
clone->len = p->len + 1;
cur->pre = q->pre = clone;
clone->size = 0;
while(p && p->ch[s] == q)
{
p->ch[s] = clone;
p = p->pre;
}
}
}
cur->size = 1; //只有原有的点有 size
last = cur;
}
long long Ans;
int main()
{
scanf("%s", s + 1);
for(R int i = 1; s[i]; i++) Add(s[i] - 'a');
for(R Data *i = b + 1; i <= b + tot; i++) i->pre->In++; b[0].In = 19260817;
for(R Data *i = b + 1; i <= b + tot; i++) if(!i->In) *(++tail) = i;
do
{
++head;
(*head)->pre->In--;
if((*head)->pre->In == 0) *(++tail) = (*head)->pre;
(*head)->pre->size += (*head)->size;
if((*head)->size > 1) Ans = Max(1ll * (*head)->size * (*head)->len, Ans);
}
while(head < tail);
printf("%lld\n", Ans);
return 0;
}