[POI 2000] 病毒

[题目链接]

https://www.lydsy.com/JudgeOnline/problem.php?id=2938

[算法]

首先建出给定字符串集的AC自动机

存在无限长的代码当且仅当 ： AC自动机上存在一个环且环上没有危险节点

时间复杂度 ： O(N)

[代码]

#include<bits/stdc++.h>
using namespace std;
#define MAXP 300010
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;

int n;
char s[MAXP];

struct AC_Automation
{
    int sz , rt , timer;
    int fail[MAXP];
    bool danger[MAXP] , vis[MAXP] , ins[MAXP];
    int child[MAXP][];
    inline void init()
    {
        timer = ;
        sz = ;
        rt = newnode();
    }
    inline void chkmin(int &x , int y)
    {
        x = min(x , y);
    }
    inline int newnode()
    {
        ++sz;
        child[sz][] = child[sz][] = -;
        fail[sz] = danger[sz] = ;
        return sz;
    }
    inline void insert(char *s)
    {
        int now = rt;
        for (int i = ; i <= strlen(s + ); i++)
        {
            int nxt = s[i] - '';
            if (child[now][nxt] == -) child[now][nxt] = newnode();
            now = child[now][nxt];
        }
        danger[now] = ;
    }
    inline void rebuild()
    {
        queue< int > q;
        fail[rt] = rt;
        for (int i = ; i < ; i++)
        {
            if (child[rt][i] == -)
                child[rt][i] = rt;
            else
            {
                fail[child[rt][i]] = rt;
                q.push(child[rt][i]);
            }
        }
        while (!q.empty())
        {
            int cur = q.front();
            q.pop();
            for (int i = ; i < ; i++)
            {
                if (child[cur][i] == -)
                    child[cur][i] = child[fail[cur]][i];
                else
                {
                    fail[child[cur][i]] = child[fail[cur]][i];
                    danger[child[cur][i]] |= danger[fail[child[cur][i]]];
                    q.push(child[cur][i]);
                }
            }
        }
    }
    inline void solve(int now)
    {
        if (ins[now])
        {
            printf("TAK\n");
            exit();
        }
        if (vis[now] || danger[now]) return;
        vis[now] = ins[now] = ;
        if (child[now][] != -) solve(child[now][]);
        if (child[now][] != -) solve(child[now][]);
        ins[now] = ;
    }
} ACAM;

template <typename T> inline void chkmin(T &x , T y) { x = min(x , y); }
template <typename T> inline void chkmax(T &x , T y) { x = max(x , y); }
template <typename T> inline void read(T &x)
{
   T f = ; x = ;
   char c = getchar();
   for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
   for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';
   x *= f;
}

int main()
{

    scanf("%d" , &n);
    ACAM.init();
    for (int i = ; i <= n; i++)
    {
        scanf("%s" , s + );
        ACAM.insert(s);
    }
    ACAM.rebuild();
    ACAM.solve();
    printf("NIE\n");

    return ;
}