topcoder srm 663 div1 -23

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstring>
using namespace std;

const int mod=1000000007;


set<string> S[55];


int check(string s) {
    return S[s.size()].find(s)!=S[s.size()].end();
}

string T;

int dfs(string a,int n) {
    if(a.size()==n) {
        return a==T;
    }
    if(check(a+‘A‘)&&dfs(a+‘A‘,n)) {
        return 1;
    }
    a+=‘B‘;
    reverse(a.begin(),a.end());
    if(check(a)&&dfs(a,n)) return 1;
    return 0;
}

class ABBADiv1
{
public:
    string canObtain(string a,string b)
    {
        for(int i=0;i<55;++i) S[i].clear();
        for(int i=0;i<(int)b.size();++i) {
            for(int j=i;j<(int)b.size();++j) {
                int L=j-i+1;
                string s=b.substr(i,L);
                S[L].insert(s);
                reverse(s.begin(),s.end());
                S[L].insert(s);
            }
        }
        T=b;
        if(dfs(a,(int)b.size())) return "Possible";
        return "Impossible";
    }
};