[Link] https://www.acmicpc.net/problem/1707
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
public static void main(String[] args) throws IOException {
StringBuilder sb = new StringBuilder();
Queue<Integer> q = new LinkedList<>();
String[] line;
int tot = toi(br.readLine());
loop:
for(int i = 0; i < tot; i++) {
q.clear();
line = br.readLine().split(" ");
int v = toi(line[0]), e = toi(line[1]);
int[] group = new int[v];
ArrayList<LinkedList<Integer>> al = new ArrayList<>();
for(int j = 0; j < v; j++) al.add(new LinkedList<Integer>());
for(int j = 0; j < e; j++) {
line = br.readLine().split(" ");
al.get(toi(line[0]) - 1).add(toi(line[1]) - 1);
al.get(toi(line[1]) - 1).add(toi(line[0]) - 1);
}
for(int j = 0; j < v; j++) {
if(group[j] == 0) {
q.add(j);
group[j] = 1;
while(!q.isEmpty()) {
int bottom = q.poll();
for(int e1: al.get(bottom)) {
if(group[e1] != 0) {
if((group[bottom] & group[e1]) != 0) {
sb.append("NO\n");
continue loop;
}
continue;
}
group[e1] = (group[bottom] & 1) + 1; // group[bottom] == 1 ? 2 : 1
q.add(e1);
}
}
}
}
sb.append("YES\n");
}
System.out.print(sb);
}
static int toi(String s) { return Integer.parseInt(s); }
}