TopCoder High School SRM 39 Level one - 250 pt - Web Browser solution

TopCoder High School SRM 39 Level one - 250 pt - Web Browser statement: http://community.topcoder.com/stat?c=problem_statement&pm=8121&rd=10782

TopCoder High School SRM 39 Level one - 250 pt - Web Browser editorial: http://community.topcoder.com/tc?module=Static&d1=hs&d2=match_editorials&d3=hs_srm39

TopCoder High School SRM 39 Level one - 250 pt - Web Browser solution: 

#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
using namespace std;

#define forn(i,n)     for(int i=0; i<int((n)); ++i)
#define forv(i,v)     forn(i,int(v.size()))
#define ALL(a)        (a).begin(),(a).end()
#define pb            push_back
#define sz            size()
#define SORT(a)       sort(ALL(a))
#define iss           istringstream
 
typedef vector< int > vi; typedef vector< string > vs;

class WebBrowser {
public:
    vector <string> getSequence(vector <string> a) {
        vector <string> ans;
  
  vs back;
  vs forw;
  string cur;
  
  forv (i,a)
  {
    if ( a[i] == "BACK" )
    {
      if ( back.sz != 0 )
      {
        if ( cur != "" )
        forw.insert(forw.begin(),cur);//,cur);
        cur = back[back.sz-1];
        back.erase(back.end()-1);
        ans.pb(cur);
      }
    }
    else
    if ( a[i] == "FORWARD" )
    {
      if ( forw.sz > 0 )
      {
        if ( cur != "" )
        back.pb(cur);
        cur = forw[0];
        forw.erase(forw.begin());
        ans.pb(cur);
      }
    }
    else
    {
      if ( cur != a[i] )
      {
        if ( cur != "" )
        back.pb(cur);
        cur = a[i];
        forw.clear();
        ans.pb(cur);
      }
    }
  }
  
        return ans;
}

};