【洛谷 P5357】 【模板】AC自动机（二次加强版）（AC自动机，差分）

每次匹配都不停跳fail显然太慢了，于是在每个节点和fail指向的点连一条边，构成一棵树，在这棵树上差分一下就好了。

AC自动机 就这个算法而言其实没用想象中那么难。

#include <cstdio>
#include <queue>
#include <cstring>
using namespace std;
struct Node{
    int fail, next[26], num;
}AC[200010];
int n, u, cnt;
queue <int> q;
int p[200010], vis[200010];
char a[2000010];
int f[200010];
struct Edge{
	int next, to;
}e[200010];
int head[200010], num;
inline void Add(int from, int to){
	e[++num].to = to; e[num].next = head[from]; head[from] = num;
}
void insert(int x){
    int len = strlen(a + 1), w;
    u = 0;
    for(int i = 1; i <= len; ++i){
        w = a[i] - 'a';
        if(!AC[u].next[w])
          AC[u].next[w] = ++cnt;
        u = AC[u].next[w];
    }
    f[x] = u;
}
void BuildFail(){
	u = 0;
    for(int i = 0; i < 26; ++i)
       if(AC[u].next[i])
         q.push(AC[u].next[i]);
    while(q.size()){
        u = q.front(); q.pop();
        for(int i = 0; i < 26; ++i)
           if(AC[u].next[i]){
           	 q.push(AC[u].next[i]);
             AC[AC[u].next[i]].fail = AC[AC[u].fail].next[i];
           }
           else
		     AC[u].next[i] = AC[AC[u].fail].next[i];
    }
}
void Match(){
    int len = strlen(a + 1);
    u = 0;
    for(int i = 1; i <= len; ++i){
        u = AC[u].next[a[i] - 'a'];
        ++vis[u];
    }
}
void dfs(int x){
	for(int i = head[x]; i; i = e[i].next){
		dfs(e[i].to); vis[x] += vis[e[i].to];
	}
}
int main(){
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i) f[i] = i;
    for(int i = 1; i <= n; ++i){
     	scanf("%s", a + 1);
    	insert(i);
    }
    scanf("%s", a + 1);
    BuildFail();
    Match();
    for(int i = 1; i <= cnt; ++i)
       Add(AC[i].fail, i);
    dfs(0);
    for(int i = 1; i <= n; ++i)
       printf("%d\n", vis[f[i]]);
    return 0;
}