P3808 【模板】AC自动机（简单版）

https://www.luogu.org/problemnew/show/P3808

　　建立AC自动机，然后在文本串扫一遍，统计每个串出现的次数。

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;

const int N = 500100;
char str[N << 1], s[110];
int ch
[26], fail
, val
, last
, q
, L, R, Index;

void Insert(char *s) {
int len = strlen(s), u = 0;
for (int i=0; i<len; ++i) {
int c = s[i] - 'a';
if (!ch[u][c]) ch[u][c] = ++Index;
u = ch[u][c];
}
val[u] ++;
}
void build() {
L = 1;R = 0;
fail[0] = 0;
for (int c=0; c<26; ++c) {
int u = ch[0][c];
if (u) fail[u] = 0, q[++R] = u, last[u] = 0;
}
while (L <= R) {
int u = q[L++];
for (int c=0; c<26; ++c) {
int v = ch[u][c];
if (!v) {
ch[u][c] = ch[fail[u]][c];
continue;
}
q[++R] = v;
int p = fail[u];
while (p && !ch
[c]) p = fail[p];
fail[v] = ch[p][c];
last[v] = val[fail[v]] ? fail[v] : last[fail[v]];
}
}
}

int find(char *s) {
int Ans = 0, u = 0, len = strlen(s);
for (int i=0; i<len; ++i) {
int c = s[i] - 'a';
u = ch[u][c];
if (val[u]) Ans += val[u], val[u] = 0;
int p = u;
while (last[p]) {
p = last[p];
if (val[p]) Ans += val[p], val[p] = 0;
}
}
return Ans;
}

int main () {
int n;
scanf("%d", &n);
while (n--) {
scanf("%s", s);
Insert(s);
}
build();
scanf("%s",str);
printf("%d\n",find(str));
return 0;
}