HDU 3065 病毒侵袭持续中（AC自动机）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3065

题意：有n个模式串，一个主串，求每个模式串在主串中出现的次数

思路：AC自动机水题，trie树中也要维护标号，再开一个num数组记录出现次数即可，扫描匹配时注意跳转fail指针和root节点。

code：

#include <cstdio>
#include <cstring>
#include <string>
#include <queue>
using namespace std;
const int KIND = 26;
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;
char str[1005][55];
char text[2000005];
int num[1005];

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

void Query()
{
    node* temp = root;
    int len = strlen(text);
    for (int i = 0; i < len; ++i)
    {
        if (text[i] < 'A' || text[i] > 'Z')
        {
            temp = root;
            continue;
        }
        int curr = text[i] - 'A';
        while (temp->next[curr] == NULL && temp != root) temp = temp->fail;
        temp = temp->next[curr];
        if (temp == NULL) temp = root;
        node* x = temp;
        while (x != root)
        {
            if (x->id != 0) ++num[x->id];
            x = x->fail;
        }
    }
}

int main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {
        L = 0;
        root = new node();
        for (int i = 1; i <= n; ++i)
        {
            scanf("%s", str[i]);
            Insert(str[i]);
        }
        Build();
        scanf("%s", text);
        memset(num, 0, sizeof(num));
        Query();
        for (int i = 1; i <= n; ++i)
        {
            if (num[i] == 0) continue;
            printf("%s: %d
", str[i], num[i]);
        }
    }
    return 0;
}

 数组实现：

#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
const int KIND = 26;
const int MAXN = 50005;
const int MAXM = 2000005;

struct Trie
{
    int next[MAXN][KIND], fail[MAXN], id[MAXN], num[MAXN];
    int root, L, n;
    int create()
    {
        for (int i = 0; i < KIND; ++i)
            next[L][i] = -1;
        id[L++] = 0;
        return L - 1;
    }
    void init()
    {
        L = 0;
        n = 0;
        root = create();
        memset(num, 0, sizeof(num));
    }
    void insert(char str[])
    {
        int now = root;
        int len = strlen(str);
        for (int i = 0; i < len; ++i)
        {
            int curr = str[i] - 'A';
            if (-1 == next[now][curr])
                next[now][curr] = create();
            now = next[now][curr];
        }
        id[now] = ++n;
    }
    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]);
                }
            }
        }
    }
    void query(char str[])
    {
        int now = root;
        int len = strlen(str);
        for (int i = 0; i < len; ++i)
        {
            if (str[i] < 'A' || str[i] > 'Z')
            {
                now = root;
                continue;
            }
            now = next[now][str[i] - 'A'];
            int temp = now;
            while (temp != root)
            {
                if (id[temp]) ++num[id[temp]];
                temp = fail[temp];
            }
        }
    }
};
Trie ac;
char str[1005][55];
char text[MAXM];
int main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {
        ac.init();
        for (int i = 1; i <= n; ++i)
        {
            scanf("%s", str[i]);
            ac.insert(str[i]);
        }
        ac.build();
        scanf("%s", text);
        ac.query(text);
        for (int i = 1; i <= n; ++i)
        {
            if (0 == ac.num[i]) continue;
            printf("%s: %d
", str[i], ac.num[i]);
        }
    }
    return 0;
}