【SPOJ】LCS

题面

https://vjudge.net/problem/SPOJ-LCS

题解

#include<cstdio>
#include<iostream>
#include<cstring>
#define ri register int
#define N 100050
using namespace std;
char s1[N],s2[N];
struct SAM{
  int ff[N<<1],len[N<<1];
  int ch[N<<1][26];
  int last,tot;
  inline void clear() {
    last=tot=1;
    memset(ch,0,sizeof(ch));
  }
  inline void extend(int c) {
    int p,np,q,nq;
    p=last;np=++tot;last=tot;len[np]=len[p]+1;
    while(p && !ch[p][c]) ch[p][c]=np,p=ff[p];
    if (!p) ff[np]=1;
    else {
      q=ch[p][c];
      if (len[q]==len[p]+1) {
        ff[np]=q;
      }
      else {
        nq=++tot;
        len[nq]=len[p]+1;
        for (ri i=0;i<26;i++) ch[nq][i]=ch[q][i]; ff[nq]=ff[q];
        ff[np]=ff[q]=nq;
        while (p && ch[p][c]==q) ch[p][c]=nq,p=ff[p];
      }
    }
  }

  inline int match() {
    int ret=0;
    int cnt=0,now=1;
    for (ri i=1,l=strlen(s2+1);i<=l;i++) {
      if (ch[now][s2[i]-'a']) {
        cnt++;
        now=ch[now][s2[i]-'a'];
        ret=max(ret,cnt);
      }
      else {
        while (now && !ch[now][s2[i]-'a']) now=ff[now];
        if (!now) {
          cnt=0;
          now=1;
          continue;
        }
        else {
          cnt=len[now]+1;
          ret=max(ret,cnt);
          now=ch[now][s2[i]-'a'];
        }
      }
    }
    return ret;
  }
} sam;

int main(){
  scanf("%s%s",s1+1,s2+1);
  sam.clear();
  for (ri i=1,l=strlen(s1+1);i<=l;i++) sam.extend(s1[i]-'a');
  printf("%d\n",sam.match());
  return 0;
}