[20250913] BOJ / G5 / 숫자고르기 / 한종욱

Ukj0ng/202509/13 BOJ G5 숫자고르기.md

@@ -0,0 +1,64 @@
+```
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    private static final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    private static int[] arr;
+    private static boolean[] visited;
+    private static Set<Integer> result;
+    private static int N;
+
+    public static void main(String[] args) throws IOException {
+        init();
+
+        result = new TreeSet<>();
+        visited = new boolean[N + 1];
+
+        for (int i = 1; i <= N; i++) {
+            if (!visited[i]) {
+                DFS(i, i, new HashSet<>());
+            }
+        }
+
+        bw.write(result.size() + "\n");
+        for (int num : result) {
+            bw.write(num + "\n");
+        }
+
+        bw.flush();
+        bw.close();
+        br.close();
+    }
+
+    private static void init() throws IOException {
+        N = Integer.parseInt(br.readLine());
+        arr = new int[N + 1];
+
+        for (int i = 1; i <= N; i++) {
+            arr[i] = Integer.parseInt(br.readLine());
+        }
+    }
+
+    private static void DFS(int current, int start, Set<Integer> path) {
+        if (visited[current]) return;
+
+        if (current == start && !path.isEmpty()) {
+            result.addAll(path);
+            for (int node : path) {
+                visited[node] = true;
+            }
+            return;
+        }
+
+        if (path.contains(current)) {
+            return;
+        }
+
+        path.add(current);
+        DFS(arr[current], start, path);
+        path.remove(current);
+    }
+}
+```