[Bzoj1195][HNOI2006]最短母串(AC自动机)

题目链接：https://www.lydsy.com/JudgeOnline/problem.php?id=1195

多个字符串匹配问题用AC自动机没跑了，建好AC自动机后，由于要求答案要最短和字典序最小，则在AC自动机上状压bfs搜索，bfs保证搜到的串长度最短，然后每次从A-Z遍历，保证搜到的字典序最小。状态压缩成在AC自动机上节点i时，包含了串的状态为j，最后状态为(1<<n)-1时停止。

偷偷懒用cin...

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int n;
bool vis[610][4100];
struct node {
    int num, st;
    string ans;
};
struct ACzd {
    int AC[610][26];
    int fail[610];
    int numend[610];
    int len, root;
    int newcode() {
        memset(AC[len], 0, sizeof(AC[len]));
        numend[len] = 0;
        return len++;
    }
    void init() {
        len = 0;
        root = newcode();
    }
    void build(char *s, int id) {
        int k = strlen(s);
        int now = root;
        for (int i = 0; i < k; i++) {
            if (AC[now][s[i] - 'A'] == 0)
                AC[now][s[i] - 'A'] = newcode();
            now = AC[now][s[i] - 'A'];
        }
        numend[now] |= (1 << id);
    }
    void get_fail() {
        fail[root] = root;
        queue<int>q;
        for (int i = 0; i < 26; i++) {
            if (AC[root][i] != 0) {
                fail[AC[root][i]] = root;
                q.push(AC[root][i]);
            }
            else
                AC[root][i] = root;
        }
        while (!q.empty()) {
            int now = q.front();
            q.pop();
            numend[now] |= numend[fail[now]];
            for (int i = 0; i < 26; i++) {
                if (AC[now][i] != 0) {
                    fail[AC[now][i]] = AC[fail[now]][i];
                    q.push(AC[now][i]);
                }
                else
                    AC[now][i] = AC[fail[now]][i];
            }
        }
    }
    string solve() {
        queue<node>q;
        int endst = (1 << n) - 1;
        q.push({ root,0,"" });
        while (!q.empty()) {
            node p = q.front();
            q.pop();
            if (p.st == endst) {
                return p.ans;
            }
            for (int i = 0; i < 26; i++) {
                int Nextnum = AC[p.num][i];
                int Nextst = p.st | numend[Nextnum];
                if (!vis[Nextnum][Nextst]) {
                    vis[Nextnum][Nextst] = 1;
                    q.push({ Nextnum,Nextst,p.ans + (char)(i + 'A') });
                }
            }
        }
    }
}AC;
char s[55];
int main() {
    ios::sync_with_stdio(0);
    while (cin >> n) {
        AC.init();
        for (int i = 0; i < n; i++) {
            cin >> s;
            AC.build(s, i);
        }
        AC.get_fail();
        string ans = AC.solve();
        cout << ans << endl;
    }
}