ZOJ 3430 Detect the Virus（AC自动机）

题目链接：http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3430

题意：给你n个编码后的模式串，和m个编码后的主串，求原来主串中含有模式串的个数

思路：首先要将模式串解码成未编码前来建立ac自动机，然后解码主串扫描统计即可。

code：

#include <cstdio>
#include <cstring>
#include <queue>
#include <set>
using namespace std;
const int KIND = 256;
const int MAXN = 32800;

struct Trie
{
    int next[MAXN][KIND], fail[MAXN], id[MAXN];
    int root, L, num;
    int create()
    {
        for (int i = 0; i < KIND; ++i)
            next[L][i] = -1;
        return L++;
    }
    void init()
    {
        L = 0;
        num = 0;
        memset(id, 0, sizeof(id));
        root = create();
    }
    void insert(unsigned char str[], int len)
    {
        int now = root;
        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(unsigned char str[], int len)
    {
        set<int>S;
        int now = root;
        for (int i = 0; i < len; ++i)
        {
            now = next[now][str[i]];
            int temp = now;
            while (temp != root)
            {
                if (id[temp]) S.insert(id[temp]);
                temp = fail[temp];
            }
        }
        return (int)S.size();
    }
};

Trie ac;
char buf[4000];
unsigned char temp[4000];
unsigned char str[2500];

unsigned char Tran(char ch)
{
    if (ch >= 'A' && ch <= 'Z') return ch - 'A';
    if (ch >= 'a' && ch <= 'z') return ch - 'a' + 26;
    if (ch >= '0' && ch <= '9') return ch - '0' + 52;
    if (ch == '+') return 62;
    return 63;
}

int Decode(int len)
{
    int k = 0;
    for (int i = 0; i < len; i += 4)
    {
        str[k++] = (temp[i]<<2)|(temp[i + 1]>>4);
        if (i + 2 < len) str[k++] = (temp[i + 1]<<4)|(temp[i + 2]>>2);
        if (i + 3 < len) str[k++] = (temp[i + 2]<<6)|(temp[i + 3]);
    }
    return k;
}

int main()
{
    int n, m;
    while (scanf("%d", &n) != EOF)
    {
        ac.init();
        for (int i = 0; i <n; ++i)
        {
            scanf("%s", buf);
            int len = strlen(buf);
            while ('=' == buf[len - 1]) --len;
            for (int j = 0; j < len; ++j) temp[j] = Tran(buf[j]);
            ac.insert(str, Decode(len));
        }
        ac.build();
        scanf("%d", &m);
        for (int i = 0; i < m; ++i)
        {
            scanf("%s", buf);
            int len = strlen(buf);
            while ('=' == buf[len - 1]) --len;
            for (int j = 0; j < len; ++j) temp[j] = Tran(buf[j]);
            printf("%d
", ac.query(str, Decode(len)));
        }
        printf("
");
    }
    return 0;
}