CF1210A Anadi and Domino

思路：

很有意思的思维题。

实现：

 #include <bits/stdc++.h>
 using namespace std;
 int check(vector<int>& v, set<pair<int, int>>& st)
 {
     int res = ;
     map<pair<int, int>, int> mp;
     for (int i = ; i <= ; i++)
     {
         for (int j = i; j <= ; j++)
         {
             mp[make_pair(i, j)] = ;
         }
     }
     for (auto it: st)
     {
         int a = v[it.first - ], b = v[it.second - ];
         pair<int, int> tmp(min(a, b), max(a, b));
         if (mp[tmp] == )
         {
             mp[tmp] = ; res++;
         }
     }
     return res;
 }
 int main()
 {
     int n, m, a, b;
     while (cin >> n >> m)
     {
         set<pair<int, int>> st;
         for (int i = ; i < m; i++)
         {
             cin >> a >> b;
             st.insert(make_pair(min(a, b), max(a, b)));
         }
         if (n <= ) { cout << m << endl; continue; }
         vector<int> a{, , , , , , };
         int maxn = ;
         do
         {
             maxn = max(maxn, check(a, st));
         } while (next_permutation(a.begin(), a.end()));
         cout << maxn << endl;
     }
     return ;
 }