题目：https://www.luogu.org/problemnew/show/T34983
思路：模拟，用两个vector代替链表。
代码：
#include<bits/stdc++.h> using namespace std; vector<string> flist; vector<string> blist; void slv(){ char opr[10]; string a="http://www.acm.org/"; while(~scanf("%s",opr)&&opr[0]!='Q'){ if(opr[0]=='V'){ blist.push_back(a); cin>>a; flist.clear(); cout<<a<<endl; } if(opr[0]=='F') { if(flist.empty()){ printf("Ignored\n"); continue; } blist.push_back(a); a=flist[flist.size()-1]; flist.pop_back(); cout<<a<<endl; } if(opr[0]=='B') { if(blist.empty()){ printf("Ignored\n"); continue; } flist.push_back(a); a=blist[blist.size()-1]; blist.pop_back(); cout<<a<<endl; } } } int main(){ slv(); return 0; }