[20251123] BOJ / G4 / 이분 그래프 / 설진영

Author: Seol-JY

Seol-JY/202511/23 BOJ G4 이분 그래프.md

@@ -0,0 +1,73 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static ArrayList<Integer>[] graph;
+    static int[] color;
+    
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringBuilder sb = new StringBuilder();
+        
+        int K = Integer.parseInt(br.readLine());
+        
+        while(K-- > 0) {
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            int V = Integer.parseInt(st.nextToken());
+            int E = Integer.parseInt(st.nextToken());
+            
+            graph = new ArrayList[V + 1];
+            color = new int[V + 1];
+            
+            for(int i = 1; i <= V; i++) {
+                graph[i] = new ArrayList<>();
+            }
+            
+            for(int i = 0; i < E; i++) {
+                st = new StringTokenizer(br.readLine());
+                int u = Integer.parseInt(st.nextToken());
+                int v = Integer.parseInt(st.nextToken());
+                graph[u].add(v);
+                graph[v].add(u);
+            }
+            
+            boolean isBipartite = true;
+            for(int i = 1; i <= V; i++) {
+                if(color[i] == 0) {
+                    if(!bfs(i)) {
+                        isBipartite = false;
+                        break;
+                    }
+                }
+            }
+            
+            sb.append(isBipartite ? "YES" : "NO").append("\n");
+        }
+        
+        System.out.print(sb);
+    }
+    
+    static boolean bfs(int start) {
+        ArrayDeque<Integer> q = new ArrayDeque<>();
+        q.offer(start);
+        color[start] = 1;
+        
+        while(!q.isEmpty()) {
+            int cur = q.poll();
+            
+            for(int next : graph[cur]) {
+                if(color[next] == 0) {
+                    color[next] = -color[cur];
+                    q.offer(next);
+                } else if(color[next] == color[cur]) {
+                    return false;
+                }
+            }
+        }
+        
+        return true;
+    }
+}
+
+```