bzoj3172 ac自动机fail树应用

记录每一个点建自动机时候的访问次数。 
 建Fail树，然后节点子树的大小即为当前点出现的次数。

#include
#include
#include
#include
#include
using namespace std;

const int maxl = 55;
const int maxn = 1e6+5;

int ch[maxn][30], flag[maxn];
int sz, root, ans = 0;
int n, fail[maxn];

inline int idx(char x) {
	return x - 'a' + 1;
}

inline void insert(char a[]) {
	int now = root;
	int l = strlen(a);
	for(int i = 0; i < l; i++) {
		int x = idx(a[i]);
		if(!ch[now][x])
			ch[now][x] = ++sz;
		now = ch[now][x]; 
	}
	flag[now]++;	
}

int q[maxn*5], head, tail;

inline void get_fail() {
	head = tail = 0;
	for(int i = 1; i <= 26; i++)
		if(ch[0][i])
			q[tail++] = ch[0][i];
			
	while(head < tail) {
		int now = q[head++];
		for(int i = 1; i <= 26; i++) {
			if(!ch[now][i]){
                ch[now][i]=ch[fail[now]][i];
     			continue;
			}
			fail[ch[now][i]] = ch[fail[now]][i];
			q[tail++] = ch[now][i];
		}
	}
}

bool vis[maxn];

void ac(char a[]) {
	int l = strlen(a), now = root;
	for(int i = 0; i < l; i++) {
		vis[now] = 1;
		int x = idx(a[i]);
		int y = ch[now][x];
		while(y && !vis[y]) {
			vis[y] = 1;
			ans += flag[y];
			y = fail[y];
		}
		now = ch[now][x];
	}
}

char s[maxn], a[maxn];

void clear() {
	ans = sz = root = 0;
	memset(ch, 0, sizeof(ch));	memset(vis, 0, sizeof(vis));
	memset(fail, 0, sizeof(fail));
	memset(flag, 0, sizeof(flag));
}

int main() {
	int T;
	scanf("%d", &T);
	while(T--) {
		clear();
		scanf("%d", &n);
		for(int i = 1; i <= n; i++) {
			scanf("%s", a);
			insert(a);
		}
		get_fail();
		scanf("%s", s);
		ac(s);
		printf("%d\n", ans);
	}
	return 0;
}

Fail神奇l的特性：所有以x节点代表的字符串结尾的字符串节点，都在x的子树中。