LCS - Longest Common Substring
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
这题就是求最长公共子串，于是我直接套用了SAM。
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 using namespace std; 5 const int MAXN=1000010; 6 struct SAM{ 7 int fa[MAXN],ch[MAXN][27],len[MAXN],cnt,last; 8 void Init() 9 { 10 last=cnt=1; 11 } 12 void Insert(int c) 13 { 14 int p=last,np=last=++cnt; 15 len[np]=len[p]+1; 16 while(!ch[p][c]&&p) 17 ch[p][c]=np,p=fa[p]; 18 if(!p)fa[np]=1; 19 else{ 20 int q=ch[p][c]; 21 if(len[q]==len[p]+1) 22 fa[np]=q; 23 else{ 24 int nq=++cnt;len[nq]=len[p]+1; 25 memcpy(ch[nq],ch[q],sizeof(ch[p])); 26 fa[nq]=fa[q];fa[q]=fa[np]=nq; 27 while(ch[p][c]==q) 28 ch[p][c]=nq,p=fa[p]; 29 } 30 } 31 } 32 }sam; 33 char str1[MAXN],str2[MAXN]; 34 int main() 35 { 36 int len1=0,len2=0,ans=0; 37 scanf("%s%s",str1,str2); 38 sam.Init(); 39 while(str1[len1]) 40 sam.Insert(str1[len1++]-'`'); 41 int node=1,tmp=0; 42 for(;str2[len2];len2++){ 43 int c=str2[len2]-'`'; 44 if(sam.ch[node][c]) 45 node=sam.ch[node][c],tmp++; 46 else{ 47 while(node&&!sam.ch[node][c]) 48 node=sam.fa[node]; 49 if(node==0) 50 node=1,tmp=0; 51 else 52 tmp=sam.len[node]+1,node=sam.ch[node][c]; 53 } 54 ans=max(ans,tmp); 55 } 56 printf("%d ",ans); 57 return 0; 58 }