SPOJ 1811. Longest Common Substring （LCS，两个字符串的最长公共子串， 后缀自动机SAM）

1811. Longest Common Substring

Problem code: LCS

A string is finite sequence of characters over a non-empty finite set Σ.

In this problem, Σ is the set of lowercase letters.

Substring, also called factor, is a consecutive sequence of characters occurrences at least once in a string.

Now your task is simple, for two given strings, find the length of the longest common substring of them.

Here common substring means a substring of two or more strings.

Input

The input contains exactly two lines, each line consists of no more than 250000 lowercase letters, representing a string.

Output

The length of the longest common substring. If such string doesn't exist, print "0" instead.

Example

Input:
alsdfkjfjkdsal
fdjskalajfkdsla

Output:
3

后缀自动机SAM的模板题。

重新搞一遍SAM

 /* ***********************************************
 Author        :kuangbin
 Created Time  :2013-9-8 23:27:46
 File Name     :F:\2013ACM练习\专题学习\后缀自动机\new\SPOJ_LCS.cpp
 ************************************************ */

 #include <stdio.h>
 #include <string.h>
 #include <iostream>
 #include <algorithm>
 #include <vector>
 #include <queue>
 #include <set>
 #include <map>
 #include <string>
 #include <math.h>
 #include <stdlib.h>
 #include <time.h>
 using namespace std;

 const int CHAR = ;
 const int MAXN = ;
 struct SAM_Node
 {
     SAM_Node *fa, *next[CHAR];
     int len;
     int id, pos;
     SAM_Node(){}
     SAM_Node(int _len)
     {
         fa = ;
         len = _len;
         memset(next,,sizeof(next));
     }
 };
 SAM_Node SAM_node[MAXN*], *SAM_root, *SAM_last;
 int SAM_size;
 SAM_Node *newSAM_Node(int len)
 {
     SAM_node[SAM_size] = SAM_Node(len);
     SAM_node[SAM_size].id = SAM_size;
     return &SAM_node[SAM_size++];
 }
 SAM_Node *newSAM_Node(SAM_Node *p)
 {
     SAM_node[SAM_size] = *p;
     SAM_node[SAM_size].id = SAM_size;
     return &SAM_node[SAM_size++];
 }
 void SAM_init()
 {
     SAM_size = ;
     SAM_root = SAM_last = newSAM_Node();
     SAM_node[].pos = ;
 }
 void SAM_add(int x,int len)
 {
     SAM_Node *p = SAM_last, *np = newSAM_Node(p->len + );
     np->pos = len;
     SAM_last = np;
     for(; p && !p->next[x];p = p->fa)
         p->next[x] = np;
     if(!p)
     {
         np->fa = SAM_root;
         return;
     }
     SAM_Node *q = p->next[x];
     if(q->len == p->len + )
     {
         np->fa = q;
         return;
     }
     SAM_Node *nq = newSAM_Node(q);
     nq->len = p->len + ;
     q->fa = nq;
     np->fa = nq;
     for(; p && p->next[x] == q; p = p->fa)
         p->next[x] = nq;
 }
 void SAM_build(char *s)
 {
     SAM_init();
     int len = strlen(s);
     for(int i = ;i < len;i++)
         SAM_add(s[i] - 'a', i+);
 }
 char str1[MAXN], str2[MAXN];
 int main()
 {
     //freopen("in.txt","r",stdin);
     //freopen("out.txt","w",stdout);
     while(scanf("%s%s",str1,str2) == )
     {
         SAM_build(str1);
         int len = strlen(str2);
         SAM_Node *tmp = SAM_root;
         int ans = ;
         int t = ;
         for(int i = ;i < len;i++)
         {
             if(tmp->next[str2[i]-'a'])
             {
                 tmp = tmp->next[str2[i]-'a'];
                 t++;
             }
             else
             {
                 while(tmp && !tmp->next[str2[i]-'a'])
                     tmp = tmp->fa;
                 if(tmp == NULL)
                 {
                     tmp = SAM_root;
                     t = ;
                 }
                 else
                 {
                     t = tmp->len + ;
                     tmp = tmp->next[str2[i]-'a'];
                 }
             }
             ans = max(ans,t);
         }
         printf("%d\n",ans);
     }
     return ;
 }