uva 1076 - Password Suspects(AC自动机+记忆化搜索)

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题目链接：uva 1076 - Password Suspects

题目大意：有一个长度为n的密码，存在m个子串，问说有多少种字符串满足，如果满足个数不大于42，按照字典序输出。

解题思路：根据子串构建AC自动机，然后记忆化搜索，dp[i][u][s]表示第i个字符，在u节点，匹配s个子串。

#include <cstdio>#include <cstring>#include <queue>#include <string>#include <vector>#include <iostream>#include <algorithm>using namespace std;typedef long long ll;const int maxn = 105;const int maxs = (1<<10)+5;const int sigma_size = 26;struct Aho_Corasick {    int sz, g[maxn][sigma_size];    int val[maxn], fail[maxn];    void init();    int idx(char ch);    void insert(char* str, int k);    void get_fail();}AC;int N, M;vector<string> vec;ll dp[30][maxn][maxs];void init () {    AC.init();    char str[20];    for (int i = 0; i < M; i++) {        cin >> str;        AC.insert(str, i);    }    AC.get_fail();    memset(dp, -1, sizeof(dp));}ll solve (int d, int u, int s) {    if (d >= N)        return s == (1<<M)-1 ? 1 : 0;    if (dp[d][u][s] != -1)        return dp[d][u][s];    ll& ret = dp[d][u][s];    ret = 0;    for (int i = 0; i < sigma_size; i++) {        int v = AC.g[u][i];        ret += solve(d + 1, v, s | AC.val[v]);    }    return ret;}void search (int d, int u, int s, string str) {    if (d >= N) {        if (s == (1<<M) - 1)            vec.push_back(str);        return;    }    if (dp[d][u][s] <= 0)        return ;    for (int i = 0; i < sigma_size; i++) {        int v = AC.g[u][i];        char ch = 'a' + i;        search(d + 1, v, s | AC.val[v], str + ch);    }}int main () {    int cas = 0;    while (scanf("%d%d", &N, &M) == 2 && N + M) {        init();        ll ans = solve(0, 0, 0);        //printf("Case %d: %lld suspects\n", ++cas, ans);        cout << "Case " << ++cas << ": " << ans << " suspects" << endl;        if (ans <= 42) {            vec.clear();            search(0, 0, 0, "");            sort(vec.begin(), vec.end());            for (int i = 0; i < vec.size(); i++)                cout << vec[i] << endl;        }    }    return 0;}void Aho_Corasick::init() {    sz = 1;    memset(g[0], 0, sizeof(g[0]));}int Aho_Corasick::idx(char ch) {    return ch - 'a';}void Aho_Corasick::insert(char* str, int k) {    int u = 0, n = strlen(str);    for (int i = 0; i < n; i++) {        int v = idx(str[i]);        if (g[u][v] == 0) {            val[sz] = 0;            memset(g[sz], 0, sizeof(g[sz]));            g[u][v] = sz++;        }        u = g[u][v];    }    val[u] |= (1<<k);}void Aho_Corasick::get_fail() {    queue<int> que;    for (int i  = 0; i < sigma_size; i++) {        int u = g[0][i];        if (u) {            fail[u] = 0;            que.push(u);        }    }    while (!que.empty()) {        int r = que.front();        que.pop();        for (int i = 0; i < sigma_size; i++) {            int u = g[r][i];            if (u == 0) {                g[r][i] = g[fail[r]][i];                continue;            }            que.push(u);            int v = fail[r];            while (v && g[v][i] == 0)                v = fail[v];            fail[u] = g[v][i];            val[u] |= val[fail[u]];        }    }}

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