lanqiao oj 1628 最短循环节问题

#include<iostream>
#include<algorithm>
#include<cstring>
 
using namespace std ; 
const int N = 1e6 +10 ;
char s[N] ;
int n ; 
int ne[N] ;
int main(){
  cin >> n ; 
  cin >> s + 1;
  int minn = 1e9 ; 
  for(int i = 2 , j = 0; i <= n ;i ++){
    while(j && s[i] != s[j+1]) j = ne[j] ;
    if(s[i] == s[j+1]){
      minn = min(minn, i - j - 1 ) ;
    }
    ne[i] = j ; 
  }
  
  cout << minn << endl ;
  return 0 ;
}