HDU 2896 病毒侵袭（AC自动机）

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=2896

题意：给你n个模式串，m个主串，求出每个主串中出现的模式串的标号。

思路：AC自动机水题，trie树中维护标号，m次扫描即可，注意点输出格式。

code：

#include <cstdio>
#include <cstring>
#include <queue>
#include <set>
using namespace std;
const int MAXN = 10005;
const int KIND = 128;

struct node
{
    int id;
    node* fail;
    node* next[KIND];
    node()
    {
        id = 0;
        fail = NULL;
        for (int i = 0; i < KIND; ++i) next[i] = NULL;
    }
};
node* root;
int L = 0;
char str[MAXN];
set<int> ans;

void Insert(char str[])
{
    node* temp = root;
    int len = strlen(str);
    for (int i = 0; i < len; ++i)
    {
        if (temp->next[str[i]] == NULL)
            temp->next[str[i]] = new node();
        temp = temp->next[str[i]];
    }
    temp->id = ++L;
}

void Build()
{
    queue<node*>Q;
    root->fail = root;
    for (int i = 0; i < KIND; ++i)
    {
        if (root->next[i] == NULL)
            root->next[i] = root;
        else
        {
            root->next[i]->fail = root;
            Q.push(root->next[i]);
        }
    }
    while (!Q.empty())
    {
        node* temp = Q.front();
        Q.pop();
        for (int i = 0; i < KIND; ++i)
        {
            if (temp->next[i] == NULL)
                temp->next[i] = temp->fail->next[i];
            else
            {
                temp->next[i]->fail = temp->fail->next[i];
                Q.push(temp->next[i]);
            }
        }
    }
}

int Query(char str[])
{
    node* temp = root;
    int len = strlen(str);
    ans.clear();
    for (int i = 0; i < len; ++i)
    {
        while (temp->next[str[i]] == NULL && temp != root) temp = temp->fail;
        temp = temp->next[str[i]];
        if (temp == NULL) temp = root;
        node* x = temp;
        while (x != root)
        {
            if (x->id != 0) ans.insert(x->id);
            x = x->fail;
        }
    }
    return ans.size();
}


int main()
{
    int n, m;
    int tot = 0;
    while (scanf("%d", &n) != EOF)
    {
        root = new node();
        for (int i = 0; i < n; ++i)
        {
            scanf("%s", str);
            Insert(str);
        }
        Build();
        scanf("%d", &m);
        for (int i = 1; i <= m; ++i)
        {
            scanf("%s", str);
            int num = Query(str);
            if (num == 0) continue;
            printf("web %d:", i);
            set<int>::iterator it;
            for (it = ans.begin(); it != ans.end(); ++it) printf(" %d", *it);
            printf("
");
            ++tot;
        }
        printf("total: %d
", tot);
    }
    return 0;
}

 数组实现：

#include <cstdio>
#include <cstring>
#include <queue>
#include <set>
using namespace std;
const int KIND = 128;
const int MAXN = 100005;
const int MAXM = 10005;

struct Trie
{
    int next[MAXN][KIND], fail[MAXN], id[MAXN];
    int root, L, num;
    set<int> ans;
    int create()
    {
        for (int i = 0; i < KIND; ++i)
            next[L][i] = -1;
        id[L++] = 0;
        return L - 1;
    }
    void init()
    {
        num = 0;
        L = 0;
        root = create();
    }
    void insert(char str[])
    {
        int now = root;
        int len = strlen(str);
        for (int i = 0; i < len; ++i)
        {
            if (-1 == next[now][str[i]])
                next[now][str[i]] = create();
            now = next[now][str[i]];
        }
        id[now] = ++num;
    }
    void build()
    {
        queue<int>Q;
        fail[root] = root;
        for (int i = 0; i < KIND; ++i)
        {
            if (-1 == next[root][i])
                next[root][i] = root;
            else
            {
                fail[next[root][i]] = root;
                Q.push(next[root][i]);
            }
        }
        while (!Q.empty())
        {
            int now = Q.front();
            Q.pop();
            for (int i = 0; i < KIND; ++i)
            {
                if (-1 == next[now][i])
                    next[now][i] = next[fail[now]][i];
                else
                {
                    fail[next[now][i]] = next[fail[now]][i];
                    Q.push(next[now][i]);
                }
            }
        }
    }
    int query(char str[])
    {
        ans.clear();
        int now = root;
        int len = strlen(str);
        for (int i = 0; i < len; ++i)
        {
            now = next[now][str[i]];
            int temp = now;
            while (temp != root)
            {
                if (id[temp]) ans.insert(id[temp]);
                temp = fail[temp];
            }
        }
        return (int)ans.size();
    }
};
Trie ac;
char str[MAXM];
int main()
{
    int n, m, tot;
    while (scanf("%d", &n) != EOF)
    {
        ac.init();
        tot = 0;
        for (int i = 0; i < n; ++i)
        {
            scanf("%s", str);
            ac.insert(str);
        }
        ac.build();
        scanf("%d", &m);
        for (int i = 1; i <= m; ++i)
        {
            scanf("%s", str);
            if (0 == ac.query(str)) continue;
            printf("web %d:", i);
            set<int>::iterator it;
            for (it = ac.ans.begin(); it != ac.ans.end(); ++it) printf(" %d", *it);
            printf("
");
            ++tot;
        }
        printf("total: %d
", tot);
    }
    return 0;
}