CF1277D Let's Play the Words?

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 set<string> st[4];
 4 bool work(set<string>& a, set<string>& b, map<string, int>& mp, vector<int>& res)
 5 {
 6     int d = a.size() - b.size();
 7     for (auto it: a)
 8     {
 9         if (res.size() == d / 2) break;
10         string tmp = it;
11         reverse(tmp.begin(), tmp.end());
12         if (b.count(tmp)) continue;
13         res.push_back(mp[it]);
14     }
15     return res.size() >= d / 2;
16 }
17 int main()
18 {
19     int t; cin >> t;
20     while (t--)
21     {
22         for (int i = 0; i < 4; i++) st[i].clear();
23         int n; cin >> n;
24         map<string, int> mp;
25         for (int i = 0; i < n; i++)
26         {
27             string s; cin >> s;
28             mp[s] = i + 1;
29             int a = *s.begin() - ‘0‘, b = *(s.end() - 1) - ‘0‘;
30             int p = a * 2 + b;
31             st[p].insert(s);
32         }
33         if (!st[0].empty() && !st[3].empty() && st[1].empty() && st[2].empty())
34         {
35             cout << -1 << endl; continue;
36         }
37         vector<int> res;
38         bool ok = false;
39         if (st[1].size() > st[2].size()) ok = work(st[1], st[2], mp, res);
40         else ok = work(st[2], st[1], mp, res);
41         if (ok)
42         {
43             cout << res.size() << endl;
44             for (auto it: res) cout << it << " ";
45             cout << endl;
46         }
47         else cout << -1 << endl;
48     }
49     return 0;
50 }