UVALive 3907 Puzzle AC自动机+DP

10天前交的题，当时OJ挂了，现在才想起去看结果。

如果在状态上深搜的过程中出现了环，说明可以无限长。

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb(a) push_back(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {
    return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {
    return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#else

    freopen("in.txt","r",stdin);
   // freopen("d:\\out1.txt","w",stdout);
#endif
}
int getch() {
    int ch;
    while((ch=getchar())!=EOF) {
        if(ch!=' '&&ch!='\n')return ch;
    }
    return EOF;
}

const int MAX_NODE=500000;
const int SIGMA_SIZE=26;

int ch[MAX_NODE][SIGMA_SIZE];
int fail[MAX_NODE];
int val[MAX_NODE];

char dmc[MAX_NODE];
int sz;
int idx(char c){return c-'A';}
void init()
{
    sz=1;
    memset(ch[0],0,sizeof(ch[0]));
    val[0]=0;
}

void insert(const char *s)
{
    int u=0;
    for(int i=0;s[i]!='\0';i++)
    {
        int c=idx(s[i]);
        if(!ch[u][c])
        {
            memset(ch[sz],0,sizeof(ch[sz]));
            val[sz]=0;
            dmc[sz]=s[i];
            ch[u][c]=sz++;
        }
        u=ch[u][c];
    }
    val[u]=1;
}

void construct()
{
    queue<int> q;
    fail[0]=0;
    for(int c=0;c<SIGMA_SIZE;c++)
    {
        int u=ch[0][c];
        if(u){fail[u]=0;q.push(u);}
    }

    while(!q.empty())
    {
        int r=q.front();q.pop();
        for(int c=0;c<SIGMA_SIZE;c++)
        {
            int u=ch[r][c];

            if(!u){ch[r][c]=ch[fail[r]][c];continue;}
            q.push(u);
            int v=fail[r];
            while(v&&!ch[v][c])v=fail[v];
            fail[u]=ch[v][c];
            val[u]|=val[fail[u]];
        }
    }
}

int n,m;

int vis[MAX_NODE];
int dp[MAX_NODE];
int road[MAX_NODE];
int flag;
int f(int u)
{
    if(vis[u]==-1)
    {
        flag=0;return 0;
    }else if(vis[u]==1)
        return dp[u];
    vis[u]=-1;
    dp[u]=0;
    for(int c=n-1;c>=0;c--)
    {
        int v=ch[u][c];
        if(!val[v])
        {
            if(f(v)+1>dp[u])
            {
                dp[u]=f(v)+1;
                road[u]=c;
            }
        }
        if(!flag)return 0;
    }
    vis[u]=1;
    return dp[u];
}
int main()
{
   // debug();
    int t;
    scanf("%d",&t);
    for(int ca=1;ca<=t;ca++)
    {
        scanf("%d%d",&n,&m);
        init();
        for(int i=1;i<=m;i++)
        {
            char buf[100];
            scanf("%s",buf);
            insert(buf);
        }
        construct();
        memset(vis,0,sizeof(vis));
        flag=1;
        int num=f(0);
        if(!flag||!num)printf("No\n");
        else
        {
            int u=0;
            while(num--)
            {
                printf("%c",road[u]+'A');
                u=ch[u][road[u]];
            }
            printf("\n");
        }
       // printf("%d %d\n",num,flag);
    }
    return 0;
}