求大佬指点

#include<bits/stdc++.h>
using namespace std;
int nxt[1000005],n;
string p,s;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>p;
		int l1=p.length(),l2=s.length();
		string ss=p;
		p+="@",p+=s,p.insert(0," ");
//		cout<<p<<" ";
		for(int i=l1+2;i<=l1+l2+1;i++) nxt[i]=0;
		for(int i=l1+l2-min(l1,l2)+2,j=0;i<=l1+l2+1;i++){
			while(p[i]!=p[j+1]&&j) j=nxt[j];
			if(p[i]==p[j+1]) j++;
			nxt[i]=j;
//			cout<<nxt[i]<<" ";
		}
		ss.erase(0,nxt[l1+l2+1]);
		s.append(ss);
	}cout<<s;
	return 0;
}