题目链接：https://codeforces.com/contest/1230/problem/C
思路：暴搜，，，，赛后一遍过，为啥当时没想到。
1 #include<iostream>
2 #include<cstdio>
3 #include<ctime>
4 #include<cstring>
5 #include<cstdlib>
6 #include<cmath>
7 #include<queue>
8 #include<stack>
9 #include<map>
10 #include<algorithm>
11 #define Max(a,b) ((a)>(b)?(a):(b))
12 #define Min(a,b) ((a)<(b)?(a):(b))
13 #define Mem0(x) memset(x,0,sizeof(x))
14 #define Mem1(x) memset(x,-1,sizeof(x))
15 #define MemX(x) memset(x,0x3f,sizeof(x))
16 using namespace std;
17 typedef long long ll;
18 const int inf=0x3f3f3f;
19 const double pi=acos(-1.0);
20
21 int cnt[30][30];
22 struct node{
23 int x,y;
24 bool flag;
25 }edge[30];
26
27 void init()
28 {
29 memset(cnt,0,sizeof(cnt));
30 for (int i=1;i<=6;i++){
31 for (int j=i;j<=6;j++){
32 cnt[i][j]++;
33 }
34 }
35 return ;
36 }
37 int node1[20],n,m,ans;
38 void dfs()
39 {
40 init();
41 node edge1[30];
42 for (int i=1;i<=m;i++){
43 edge1[i].x=edge[i].x;
44 edge1[i].y=edge[i].y;
45 edge1[i].flag=false;
46 }
47 int tmp=0;
48 for (int i=1;i<=m;i++){
49 if (cnt[node1[edge1[i].x]][node1[edge1[i].y]]>0){
50 cnt[node1[edge1[i].x]][node1[edge1[i].y]]--;
51 tmp++;
52 }
53 }
54 ans=max(tmp,ans);
55 return ;
56 }
57 void find(int pos)
58 {
59 if (pos==n+1){
60 dfs();
61 return ;
62 }
63 for (int i=1;i<=6;i++){
64 node1[pos]=i;
65 find(pos+1);
66 }
67 return ;
68 }
69 int main()
70 {
71 ans=0;
72 cin>>n>>m;
73 for (int i=1;i<=m;i++){
74 cin>>edge[i].x>>edge[i].y;
75 if (edge[i].x>edge[i].y){
76 int temp=edge[i].x;
77 edge[i].x=edge[i].y;
78 edge[i].y=temp;
79 }
80 }
81 find(0);
82 cout<<ans<<endl;
83 return 0;
84 }