洛谷-P3808-【模板】AC自动机（简单版）

题目传送门

-------------------------------------- 过年在家无聊补一下这周做的几道AC自动机的模板题

sol:标准AC自动机，注意不能重复跳fail边，像"aaaaaaa...aaaaaaaa"这样的数据每跳一次fail边只往上走了一层。

• AC自动机

  #include <bits/stdc++.h>
  using namespace std;
  typedef long long LL;
  typedef pair<int, int> PII;
  const int MAXN = 1e6 + 10;
  struct Trie {
      int son[MAXN][26], cnt[MAXN], fail[MAXN];
      int tot, root;
      int add_node() {
          int i = tot ++;
          memset(son[i], -1, sizeof(son[i]));
          cnt[i] = 0;
          return i;
      }
      void init() {
          tot = 0;
          root = add_node();
      }
      void insert(char* s) {
          int p = root;
          for (int i = 0; s[i]; i++) {
              int index = s[i] - 'a';
              if (son[p][index] == -1)
                  son[p][index] = add_node();
              p = son[p][index];
          }
          cnt[p] ++;
      }
      void build() {
          queue<int> que; fail[root] = root;
          for (int i = 0; i < 26; i++) {
              if (son[root][i] == -1) son[root][i] = root;
              else {
                  fail[son[root][i]] = root;
                  que.push(son[root][i]);
              }
          }
          while (!que.empty()) {
              int p = que.front(); que.pop();
              for (int i = 0; i < 26; i++) {
                  if (son[p][i] == -1) son[p][i] = son[fail[p]][i];
                  else {
                      fail[son[p][i]] = son[fail[p]][i];
                      que.push(son[p][i]);
                  }
              }
          }
      }
      int slove(char* s) {
          int p = root, res = 0;
          for (int i = 0; s[i]; i++) {
              int index = s[i] - 'a';
              p = son[p][index];
              for (int tmp = p; tmp != root && cnt[tmp] != -1; tmp = fail[tmp]) {
                  res += cnt[tmp];
                  // 访问过就把cnt设置成-1，防止下次跳fail边重复进入
                  cnt[tmp] = -1;
              }
          }
          return res;
      }
  } ac;
  char s[MAXN];
  int main() {
      ac.init();
      int n; scanf("%d", &n);
      for (int i = 1; i <= n; i++) {
          scanf("%s", s);
          ac.insert(s);
      }
      scanf("%s", s); ac.build();
      printf("%d
  ", ac.slove(s));
      return 0;
  }