思路

考虑一个匹配的过程，当一个节点x向后拼接一个c的时候，为了满足题目条件的限制，应该向suflink中最深的len[x]+1>=k的节点转移（保证该后缀拼上一个c之后，长度为k的子串依然属于模板串的子串），然后拓扑求最长链即可，出现环就输出INF

代码

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;
int Nodecnt,trans[250000][26],suflink[250000],maxlen[250000],n,k;
char s[250000];
int New_state(int _maxlen,int *_trans,int _suflink){++Nodecnt;maxlen[Nodecnt]=_maxlen;if(_trans)for(int i=0;i<26;i++)trans[Nodecnt][i]=_trans[i];suflink[Nodecnt]=_suflink;return Nodecnt;
}
int add_len(int u,int c){if(trans[u][c]){int v=trans[u][c];if(maxlen[v]==maxlen[u]+1){return v;}int y=New_state(maxlen[u]+1,trans[v],suflink[v]);suflink[v]=y;while(u&&trans[u][c]==v){trans[u][c]=y;u=suflink[u];}return y;}else{int z=New_state(maxlen[u]+1,NULL,0);while(u&&trans[u][c]==0){trans[u][c]=z;u=suflink[u];}if(!u){suflink[z]=1;return z;}int v=trans[u][c];if(maxlen[v]==maxlen[u]+1){suflink[z]=v;return z;}int y=New_state(maxlen[u]+1,trans[v],suflink[v]);suflink[z]=suflink[v]=y;while(u&&trans[u][c]==v){trans[u][c]=y;u=suflink[u];}return z; }
}
int in[250000],use[250000],v[250000],nxt[250000],fir[250000],cnt,dp[250000];
void init(void){Nodecnt=1;memset(trans,0,sizeof(trans));memset(suflink,0,sizeof(suflink));memset(maxlen,0,sizeof(maxlen));memset(in,0,sizeof(in));memset(use,0,sizeof(use));cnt=0;memset(v,0,sizeof(v));memset(nxt,0,sizeof(nxt));memset(fir,0,sizeof(fir));memset(dp,0,sizeof(dp));
}
void addedge(int ui,int vi){++cnt;v[cnt]=vi;nxt[cnt]=fir[ui];fir[ui]=cnt;
}
void dfs(int u){if(use[u]){for(int i=0;i<26;i++){if(trans[u][i]&&use[trans[u][i]])in[trans[u][i]]++;else{int p=u;while(p&&(trans[p][i]==0||maxlen[p]+1<k))p=suflink[p];trans[u][i]=trans[p][i];in[trans[p][i]]++;}}for(int i=fir[u];i;i=nxt[i])dfs(v[i]);}elsefor(int i=fir[u];i;i=nxt[i])dfs(v[i]);
}
queue<int> q;
int topu(void){while(!q.empty())q.pop();for(int i=1;i<=Nodecnt;i++)use[i]=(maxlen[i]>=k),addedge(suflink[i],i);dfs(1);int num=0;for(int i=1;i<=Nodecnt;i++){num+=use[i];if(use[i]&&(!in[i]))q.push(i),dp[i]=maxlen[i];}if(!num)return k-1;if(q.empty())return 0x3f3f3f3f;while(!q.empty()){int x=q.front();q.pop();for(int i=0;i<26;i++){if(trans[x][i]){dp[trans[x][i]]=max(dp[trans[x][i]],dp[x]+1);in[trans[x][i]]--;if(!in[trans[x][i]])q.push(trans[x][i]);}}}int ans=0;for(int i=1;i<=Nodecnt;i++)if(use[i]&&in[i])return 0x3f3f3f3f;elseans=max(ans,dp[i]);return ans;
}
int main(){while(scanf("%d %d",&n,&k)==2){init();for(int i=1;i<=n;i++){scanf("%s",s+1);int len=strlen(s+1),last=1;for(int j=1;j<=len;j++)last=add_len(last,s[j]-'a');}int t=topu();if(t==0x3f3f3f3f){printf("INF\n");}else{printf("%d\n",t);}}return 0;
}