#include<bits/stdc++.h>
using namespace std;
set<int>getRem(set<int>st1, set<int>st2) {
for (auto i : st2) {
st1.erase(i);
}
return st1;
}
int main() {//原则：所有不与自己连通的点必须和自己连接相同的点。
int T;
cin >> T;
for (int i = 0; i<T; ++i) {
int N, M;
cin >> N >> M;
map<int, set<int>>work;
set<int>data;
for (int k = 1; k <= N; ++k) {
data.insert(k);
}
for (int j = 0; j<M; ++j) {
int a, b;
cin >> a >> b;
work[a].insert(b);
work[b].insert(a);
}
bool flag = true;
while (data.size()>1) {
auto point = work.begin();
set<int>rems = getRem(data, point->second);
for (auto rem : rems) {
if (work[rem] != point->second) {
flag = false;
break;
}
}
if (!flag)
break;
for (auto self : rems) {
data.erase(self);
work.erase(self);
}
for (auto rest : data)
for (auto rem : rems)
work[rest].erase(rem);
}
if (flag)
cout << "YES" << endl;
else
cout << "NO" << endl;
}
system("pause");
return 0;
}/*
根本不用 dfs， bfs 直接两个 for 循环就行
注意理解题意
我这个 直接 AC 100%， 没有经过 55% 什么中间过程
*/
import java.util.*;
public class Main {
public static class Node{
public int value;
public ArrayList<Node> nexts;
public boolean pass;
public Node(int value){
this.value = value;
nexts = new ArrayList<>();
pass = false;
}
}
public static void process(Scanner in){
int n = in.nextInt();
int m = in.nextInt();
HashMap<Integer, Node> map = new HashMap<>();
for(int i = 0; i < n; i++){
map.put(i+1, new Node(i+1));
}
for(int i = 0; i < m; i++){
int f = in.nextInt();
int s = in.nextInt();
Node nf = map.get(f);
Node ns = map.get(s);
nf.nexts.add(ns);
ns.nexts.add(nf);
}
Node n1 = map.get(1);
map.remove(1);
List<Node> xl = n1.nexts;
List<Node> nxl = new ArrayList<>();
for (Map.Entry<Integer, Node> entry : map.entrySet()) {
if(!xl.contains(entry.getValue())){
nxl.add(entry.getValue());
}
}
boolean pan = false;
for(Node node : nxl){
for(Node node1: xl){
if(!node.nexts.contains(node1)){
pan = true;
break;
}
}
}
if(pan){
System.out.println("No");
}else{
System.out.println("Yes");
}
}
public static void main(String[] args){
Scanner in = new Scanner(System.in);
int n = in.nextInt();
for(int i = 0; i < n; i++){
process(in);
}
}
}
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