基本操作：
1 #include<iostream>
2 #include<unordered_set>
3 using namespace std;
4
5 unordered_set<int> s;
6
7 int main(){
8 int n = 10;
9 for(int i = 1 ; i <= n ; i++){
10 s.insert(3);
11 }
12 s.insert(4);
13 cout << (int)s.size() << endl;
14 cout << (int)s.count(3) << endl;
15 cout << *s.find(3) << endl;
16 int sz = s.count(3);
17 while(sz){
18 s.erase(3);
19 sz--;
20 }
21 cout << *s.begin() << endl;
22
23 if(s.find(3) == s.end()){
24 cout << "Not Found" << endl;
25 }
26
27
28 return 0;
29 }
运行结果：
2
1
3
4
Not Found
CF 1349B
1 #include<iostream>
2 #include<cstring>
3 #include<string>
4 #include<cstdio>
5 #include<cmath>
6 #include<queue>
7 #include<unordered_set>
8 #include<vector>
9 #define ll long long
10 using namespace std;
11
12 const int N = 1e5 + 10;
13
14 int n, m, k;
15 int deg[N];//度数
16 bool used[N];//队列内元素
17 unordered_set<int> s[N];
18
19 int read(){
20 char ch=getchar();int x=0,f=1;
21 while(ch<'0' || ch>'9') {if(ch=='-')f=-1;ch=getchar();}
22 while(ch>='0' && ch<='9'){x=x*10+ch-'0';ch=getchar();}
23 return x*f;
24 }
25
26 void init()
27 {
28 for(int i = 1 ; i <= n ; i++){
29 used[i] = false;
30 deg[i] = 0;
31 s[i].clear();
32 }
33 }
34
35 inline bool check(int u)
36 {
37 for(register int v : s[u]){
38 for(register int w : s[u]){
39 if(v == w) continue;
40 if(!s[v].count(w)) return false;
41 }
42 }
43 return true;
44 }
45
46 int main(){
47 ios::sync_with_stdio(0); cin.tie(0);
48 int T = read();
49 while(T--)
50 {
51 n = read();
52 m = read();
53 k = read();
54 init();
55
56 for(int i = 1 ; i <= m ; i++){
57 int u = read(), v = read();
58 s[u].insert(v);
59 s[v].insert(u);
60 deg[u]++;
61 deg[v]++;
62 }
63 if(1ll * k * (k - 1) > (m << 1)){//边的数量不合法
64 cout << -1 << endl;
65 continue;
66 }
67 if(k == 1){//特判
68 cout << 2 << endl << 1 << endl;
69 continue;
70 }
71 queue<int> q;
72 for(int i = 1 ; i <= n ; i++){
73 if(deg[i] < k){
74 q.push(i);
75 used[i] = true;
76 }
77 }
78 bool flag = false;
79 while(!q.empty()){
80 int u = q.front();
81 q.pop();
82 if(deg[u] == k - 1){
83 if(check(u)){
84 cout << 2 << endl;
85 for(auto v : s[u]) cout << v << ' ';
86 cout << u << endl;
87 flag = true;
88 break;
89 }
90 }
91 while(!s[u].empty()){
92 int v = *s[u].begin();
93 s[u].erase(v);
94 s[v].erase(u);
95 deg[u]--;
96 deg[v]--;
97 if(deg[v] < k && !used[v]){
98 q.push(v);
99 used[v] = true;//放进队列等待处理
100 }
101 }
102 }
103 if(flag) continue;
104 vector<int> ans;
105 for(register int i = 1 ; i <= n ; i++){
106 if(!used[i]) ans.push_back(i);
107 }
108 if(ans.empty()){
109 cout << -1 << endl;
110 }else{
111 cout << 1 << " " << (int)ans.size() << endl;
112 for(auto u : ans){
113 cout << u << " ";
114 }
115 cout << endl;
116 }
117 }
118 return 0;
119 }