• poj4052


    题意:求一个文章(长度5.1e6)里面出现了多少个指定的模式串。重复出现只记一次。而且如果两个模式串都出现的情况下,一个是另一个的子串,则该子串不算出现过。

    分析:AC自动机。

    由于子串不算所以加一些特殊处理:

    1.在文章匹配过程中,如果出现了一个模式串我们不是把匹配数量+1,而是记录那个出现过vis[id] = true;,当然trie树种也是记录了模式串的id。

    2.在匹配结束后,我们遍历所有出现过的模式串,在Trie树种找到其所有出现过的子串并将其标为未出现过vis[id] = false;

    要如何查找子串呢?

    只需要记录每个出现过的串所对应的Trie树中的节点位置,由该节点向上走到root。其间走过的每个节点都沿着fail指针走到root一次。这样二重循环遍历到的所有节点就对应了Trie中所有该模式串的子串。

    因为在AC自动机中父节点指针就是找前缀,fail指针就是找后缀。

    #include <cstdio>
    #include <cstring>
    #include <queue>
    #include <algorithm>
    #include <cctype>
    using namespace std;
    
    #define D(x)
    const int MAX_LEN = (int)(5.1e6) + 10;
    const int MAX_N = 2505;
    const int MAX_FINGER_LEN = 1105;
    const int MAX_CHILD_NUM = 26;
    const int MAX_NODE_NUM = MAX_N * MAX_FINGER_LEN;
    
    int n;
    char st[MAX_LEN];
    char st2[MAX_LEN];
    int vis[MAX_N];
    bool check[MAX_NODE_NUM];
    
    struct Trie
    {
        int next[MAX_NODE_NUM][MAX_CHILD_NUM];
        int fail[MAX_NODE_NUM];
        int count[MAX_NODE_NUM];
        int father[MAX_NODE_NUM];
        int node_cnt;
        int root;
    
        void init()
        {
            node_cnt = 0;
            root = newnode();
        }
    
        int newnode()
        {
            for (int i = 0; i < 26; i++)
                next[node_cnt][i] = -1;
            count[node_cnt++] = 0;
            return node_cnt - 1;
        }
    
        int get_id(char a)
        {
            return a - 'A';
        }
    
        void insert(char buf[], int index)
        {
            int len = strlen(buf);
            int now = root;
            for (int i = 0; i < len; i++)
            {
                int id = get_id(buf[i]);
                if (next[now][id] == -1)
                {
                    next[now][id] = newnode();
                    father[next[now][id]] = now;
                }
                now = next[now][id];
            }
            count[now] = index;
        }
    
        void build()
        {
            queue<int>Q;
            fail[root] = root;
            father[root] = root;
            for (int i = 0; i < 26; i++)
                if (next[root][i] == -1)
                    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 < 26; i++)
                    if (next[now][i] == -1)
                        next[now][i] = next[fail[now]][i];
                    else
                    {
                        fail[next[now][i]]=next[fail[now]][i];
                        Q.push(next[now][i]);
                    }
            }
        }
    
        int query(char buf[])
        {
            int now = root;
            int res = 0;
            for (int i = 0; buf[i]; i++)
            {
                now = next[now][get_id(buf[i])];
                int temp = now;
                while (temp != root && !check[temp])
                {
                    if (count[temp] != 0)
                        vis[count[temp]] = temp;
                    check[temp] = true;
                    temp = fail[temp];
                }
            }
            return res;
        }
    
        void debug()
        {
            for(int i = 0;i < node_cnt;i++)
            {
                printf("id = %3d,fail = %3d,end = %3d,chi = [",i,fail[i],count[i]);
                for(int j = 0;j < 26;j++)
                    printf("%2d",next[i][j]);
                printf("]
    ");
            }
        }
    
        void cal()
        {
            for (int i = 1; i <= n; i++)
            {
                if (vis[i] == 0)
                {
                    continue;
                }
                int temp = vis[i];
                while (temp != root)
                {
                    int temp2 = temp;
                    while (temp2 != root && !check[temp2])
                    {
                        if (count[temp2] != 0 && count[temp2] != i)
                        {
                            vis[count[temp2]] = 0;
                            check[temp2] = true;
                        }
                        temp2 = fail[temp2];
                    }
                    temp = father[temp];
                }
            }
        }
    };
    
    Trie ac;
    
    void transform(char st[], char st2[])
    {
        int len = 0;
        for (int i = 0; st[i]; i++)
        {
            if (isupper(st[i]))
            {
                st2[len++] = st[i];
                continue;
            }
            i++;
            int temp = 0;
            while (isdigit(st[i]))
            {
                temp *= 10;
                temp += st[i] - '0';
                i++;
            }
            for (int j = 0; j < temp; j++)
            {
                st2[len + j] = st[i];
            }
            len += temp;
            i++;
        }
        st2[len] = 0;
    }
    
    void input()
    {
        scanf("%d", &n);
        for (int i = 1; i <= n; i++)
        {
            scanf("%s", st);
            transform(st, st2);
            ac.insert(st2, i);
        }
    }
    
    int work()
    {
        memset(vis, 0, sizeof(vis));
        memset(check, 0, sizeof(check));
        ac.query(st2);
        memset(check, 0, sizeof(check));
        ac.cal();
        int ret = 0;
        for (int i = 1; i <= n; i++)
        {
            if (vis[i])
            {
                D(printf("#%d
    ", vis[i]));
                ret++;
            }
        }
        return ret;
    }
    
    int main()
    {
        int t;
        scanf("%d", &t);
        while (t--)
        {
            ac.init();
            input();
            ac.build();
            scanf("%s", st);
            transform(st, st2);
            printf("%d
    ", work());
        }
        return 0;
    }
    View Code
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  • 原文地址:https://www.cnblogs.com/rainydays/p/4331649.html
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