[20250305] BOJ / P5 / Cards Flipping / 권혁준

Author: oncsr

khj20006/202503/05 BOJ P5 Cards Flipping.md

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+```java
+
+import java.util.*;
+import java.io.*;
+
+class Main {
+	
+	// IO field
+	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+	static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+	static StringTokenizer st;
+
+	static void nextLine() throws Exception {st = new StringTokenizer(br.readLine());}
+	static int nextInt() {return Integer.parseInt(st.nextToken());}
+	static long nextLong() {return Long.parseLong(st.nextToken());}
+	static void bwEnd() throws Exception {bw.flush();bw.close();}
+	
+	// Additional field
+
+	static List<Integer>[] V;
+	static int N;
+	static int[] A, B;
+	static boolean[] vis;
+	static int ans = 0, cnt = 0;
+	static boolean multiedge;
+	
+	public static void main(String[] args) throws Exception {
+		
+		ready();
+		solve();
+	
+		bwEnd();
+		
+	}
+	
+	static void ready() throws Exception{
+
+		N = Integer.parseInt(br.readLine());
+		A = new int[N];
+		B = new int[N];
+		
+		nextLine();
+		for(int i=0;i<N;i++) A[i] = nextInt();
+		
+		nextLine();
+		for(int i=0;i<N;i++) B[i] = nextInt();
+
+		vis = new boolean[1000001];
+		V = new List[1000001];
+		
+		for(int i=0;i<=1000000;i++) V[i] = new ArrayList<>();
+		
+		for(int i=0;i<N;i++) {
+			V[A[i]].add(B[i]);
+			V[B[i]].add(A[i]);	
+		}
+		
+		for(int i=0;i<=1000000;i++) if(!V[i].isEmpty()) Collections.sort(V[i]);
+		
+	}
+	
+	static void solve() throws Exception{
+
+		for(int i=0;i<=1000000;i++) {
+			if(vis[i]) continue;
+			multiedge = false;
+			cnt = 0;
+			vis[i] = true;
+			if(dfs(i, -1) && !multiedge) ans += cnt-1;
+			else ans += cnt;
+		}
+		bw.write(ans + "\n");
+		
+	}
+	
+	// 트리면 true, 아니면 false
+	static boolean dfs(int n, int p) {
+		cnt++;
+		boolean res = true;
+		int prev = -1;
+		for(int i=0;i<V[n].size();i++) if(!V[n].get(i).equals(p)) {
+			int x = V[n].get(i);
+			if(i < V[n].size()-1 && V[n].get(i+1).equals(x)) multiedge = true;
+			if(vis[x]) res = false;
+			else{
+				vis[x] = true;
+				res &= dfs(x,n);
+			}
+		}
+		return res;
+	}
+	
+	
+}
+
+```