SPOJ 1811LCS Longest Common Substring

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Longest Common Substring

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Description

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

Notice: new testcases added

Source

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#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int CHAR=26,maxn=251000;

struct SAM_Node
{
    SAM_Node *fa,*next[CHAR];
    int len,id,pos;
    SAM_Node(){}
    SAM_Node(int _len)
    {
        fa=0; len=_len;
        memset(next,0,sizeof(next));
    }
};

SAM_Node SAM_node[maxn*2],*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=0;
    SAM_root=SAM_last=newSAM_Node(0);
    SAM_node[0].pos=0;
}

void SAM_add(int x,int len)
{
    SAM_Node *p=SAM_last,*np=newSAM_Node(p->len+1);
    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+1)
    {
        np->fa=q;
        return ;
    }
    SAM_Node *nq=newSAM_Node(q);
    nq->len=p->len+1;
    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=0;i<len;i++)
        SAM_add(s[i]-'a',i+1);
}

char A[maxn],B[maxn];

int main()
{
    scanf("%s%s",A,B);
    SAM_build(A);
    int m=strlen(B),ans=0,temp=0;
    SAM_Node *now=SAM_root;
    for(int i=0;i<m;i++)
    {
        int c=B[i]-'a';
        if(now->next[c])
        {
            now=now->next[c];
            temp++;
        }
        else
        {
            while(now&&!now->next[c])
                now=now->fa;
            if(now)
            {
                temp=now->len+1;
                now=now->next[c];
            }
            else
            {
                temp=0;
                now=SAM_root;
            }
        }
        ans=max(ans,temp);
    }
    printf("%d\n",ans);
    return 0;
}

SPOJ 1811LCS Longest Common Substring