SPOJ-LCS Longest Common Substring 【后缀自动机】

题目分析：

用没出现过的字符搞拼接。搞出right树，找right集合的最小和最大。如果最小和最大分居两侧可以更新答案。

代码：

 #include<bits/stdc++.h>
 using namespace std;

 const int maxn = ;

 int son[maxn][],fa[maxn],maxlen[maxn],root,num,sigma = ;
 int minn[maxn],maxx[maxn];// lright rright

 string str,ss;
 int n,m;
 vector<int> T[maxn];

 int addnew(int dt){maxlen[++num] = dt;return num;}
 int ins(char x,int p,int hhhh){
     int np = addnew(maxlen[p]+); minn[np] = maxx[np] = hhhh;
     while(p && !son[p][x-'a']) son[p][x-'a'] = np,p = fa[p];
     if(!p){fa[np] = root; return np;}
     else{
     int q = son[p][x-'a'];
     if(maxlen[q]==maxlen[p]+){fa[np]=q;return np;}
     else{
         int nq = addnew(maxlen[p]+);
         for(int i=;i<sigma;i++) son[nq][i] = son[q][i];
         fa[nq] = fa[q]; fa[q] = fa[np] = nq;
         while(p && son[p][x-'a'] == q) son[p][x-'a'] = nq,p = fa[p];
         return np;
     }
     }
 }

 void dfs(int now){
     if(!minn[now]) minn[now] = 1e9;
     for(int i=;i<T[now].size();i++){
     dfs(T[now][i]);
     minn[now] = min(minn[now],minn[T[now][i]]);
     maxx[now] = max(maxx[now],maxx[T[now][i]]);
     }
 }

 void work(){
     int lst = addnew();root = lst;
     for(int i=;i<str.length();i++)
     lst = ins(str[i],lst,i+);
     for(int i=;i<=num;i++) T[fa[i]].push_back(i);
     dfs(); int ans = ;
     for(int i=;i<=num;i++)if(minn[i]<=n&&maxx[i]>n+)ans=max(ans,maxlen[i]);
     cout<<ans<<endl;
 }

 int main(){
     ios::sync_with_stdio(false);
     cin.tie();
     cin >> str; cin >> ss;
     n = str.length(); m = ss.length();
     str += ('z'+); str += ss;
     work();
     return ;
 }