[20251123] BOJ / G4 / 이분 그래프 / 이종환

Author: 0224LJH

0224LJH/202511/23 BOJ 이분 그래프.md

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+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.PriorityQueue;
+import java.util.Queue;
+import java.util.StringTokenizer;
+
+public class Main {
+	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+	static StringBuilder sb = new StringBuilder();
+	static int nodeCnt, edgeCnt;
+	static String ans;
+	static Node[] nodes;
+	static boolean[] visited;
+	
+	static class Node{
+		int num;
+		int team = 0;
+		HashSet<Node> set = new HashSet<>();
+		public Node(int num) {
+			this.num = num;
+		}
+	}
+
+	
+    public static void main(String[] args) throws IOException {
+    	int tc = Integer.parseInt(br.readLine());
+    	for (int i = 0; i < tc; i++) {
+        	init();
+        	process();
+        	sb.append(ans).append("\n");
+    	}
+    	print();
+
+    }
+    
+    private static void init() throws IOException{
+    	StringTokenizer st = new StringTokenizer(br.readLine());
+    	nodeCnt = Integer.parseInt(st.nextToken());
+    	edgeCnt = Integer.parseInt(st.nextToken());
+    	
+    	nodes = new Node[nodeCnt+1];
+    	visited = new boolean[nodeCnt+1];
+    	
+    	for (int i = 1; i <= nodeCnt; i++) {
+    		nodes[i] = new Node(i);
+    	}
+    	for (int i = 0; i < edgeCnt; i++) {
+    		st = new StringTokenizer(br.readLine());
+    		Node from = nodes[Integer.parseInt(st.nextToken())];
+    		Node to = nodes[Integer.parseInt(st.nextToken())];
+    		from.set.add(to);
+    		to.set.add(from);
+    	}
+    	
+    }
+    
+    private static void process() throws IOException {
+    	ans = "YES";
+    	for (int i = 1; i <= nodeCnt; i++) {
+    		Node target = nodes[i];
+    		if (visited[target.num]) continue;
+    		processRound(target.num);
+    		
+    		
+    	}
+
+
+    	
+
+    }
+    
+    private static void processRound(int idx) {
+    	nodes[idx].team = idx;
+    	Queue<Node> q = new LinkedList<>();
+    	q.add(nodes[idx]);
+    	while(!q.isEmpty()) {
+    		Node n = q.poll();
+    		if (visited[n.num]) continue;
+    		visited[n.num] = true;
+    		
+    		int opp = n.team*(-1);
+    		
+    		for (Node node: n.set) {
+    			if(node.team == 0) {
+    				node.team = opp;
+    				q.add(node);
+    			} else if (node.team == opp) {
+    				continue;
+    			}else {
+    				ans = "NO";
+    				return;
+    			}
+    			
+    			
+    		}
+    		
+    	}
+    	
+    }
+    
+    
+
+	private static void print() {
+		System.out.print(sb.toString());
+    }
+
+}
+```