CF1277D Let's Play the Words?

思路：

字符串其实只有0...0, 0...1, 1...0, 1...1四种。

实现：

 #include <bits/stdc++.h>
 using namespace std;
 set<string> st[];
 bool work(set<string>& a, set<string>& b, map<string, int>& mp, vector<int>& res)
 {
     int d = a.size() - b.size();
     for (auto it: a)
     {
         if (res.size() == d / ) break;
         string tmp = it;
         reverse(tmp.begin(), tmp.end());
         if (b.count(tmp)) continue;
         res.push_back(mp[it]);
     }
     return res.size() >= d / ;
 }
 int main()
 {
     int t; cin >> t;
     while (t--)
     {
         for (int i = ; i < ; i++) st[i].clear();
         int n; cin >> n;
         map<string, int> mp;
         for (int i = ; i < n; i++)
         {
             string s; cin >> s;
             mp[s] = i + ;
             int a = *s.begin() - '', b = *(s.end() - ) - '';
             int p = a *  + b;
             st[p].insert(s);
         }
         if (!st[].empty() && !st[].empty() && st[].empty() && st[].empty())
         {
             cout << - << endl; continue;
         }
         vector<int> res;
         bool ok = false;
         if (st[].size() > st[].size()) ok = work(st[], st[], mp, res);
         else ok = work(st[], st[], mp, res);
         if (ok)
         {
             cout << res.size() << endl;
             for (auto it: res) cout << it << " ";
             cout << endl;
         }
         else cout << - << endl;
     }
     return ;
 }