AC自动机 再理解 +模板

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本文链接： https://blog.csdn.net/weixin_44510468/article/details/102641726

模板

class Aho_Corasick { 
public:
    static const int MAXN = 1e4*50+10;
	int nxt[MAXN][26], fail[MAXN], end[MAXN];
	int root, L;
    Aho_Corasick ( ) { };
	int newnode ( ) {
		for ( int i = 0; i < 26; i++ )
			nxt[L][i] = -1;
		end[L++] = 0;
		return L-1;
	}
	void init ( ) { // 先初始化
		L = 0;
		root = newnode ( );
	}
	void insert ( char buf[] ) { // 再插入多个模式串构成字典树
		int len = strlen ( buf );
		int now = root;
		for ( int i = 0; i < len; i++ ) {
			if ( nxt[now][buf[i] - 'a'] == -1 )
				nxt[now][buf[i] - 'a'] = newnode ( );
			now = nxt[now][buf[i] - 'a'];
		}
		end[now]++;
	}
	void build ( ) { // 然后给树建立失配指针
		queue<int>Q;
		fail[root] = root;
		for ( int i = 0; i < 26; i++ )
			if ( nxt[root][i] == -1 )
				nxt[root][i] = root;
			else {
				fail[nxt[root][i]] = root;
				Q.push ( nxt[root][i] );
			}
		while ( !Q.empty ( ) ) {
			int now = Q.front ( );
			Q.pop ( );
			for ( int i = 0; i < 26; i++ )
				if ( nxt[now][i] == -1 )
					nxt[now][i] = nxt[fail[now]][i];
				else {
					fail[nxt[now][i]] = nxt[fail[now]][i];
					Q.push ( nxt[now][i] );
				}
		}
	}
	long long query ( char buf[] ) { // 查询模式串在文本串出现次数前需要先构建 build 构建适配指针
		int len = strlen ( buf ), now = root; long long res = 0;
		for ( int i = 0; i < len; i++ ) {
			now = nxt[now][buf[i] - 'a'];
			int temp = now;
			while ( temp != root ) {
				res += end[temp];
				end[temp] = 0;
				temp = fail[temp];
			}
		}
		return res;
	}
}ac;

理解

一个详细讲解的博客
另一个详解的博客
一篇非常详细的讲ac自动机的博客
kuangbin大神的AC自动机总结