[20251011] BOJ / G5 / 숫자고르기 / 강신지

ksinji/202510/11 BOJ G5 숫자고르기.md

@@ -0,0 +1,54 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static int N;
+    static int[] num;
+    static boolean[] visited;
+    static boolean[] finished;
+    static List<Integer> result = new ArrayList<>();
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        N = Integer.parseInt(br.readLine());
+        num = new int[N + 1];
+        visited = new boolean[N + 1];
+        finished = new boolean[N + 1];
+
+        for (int i = 1; i <= N; i++) {
+            num[i] = Integer.parseInt(br.readLine());
+        }
+
+        for (int i = 1; i <= N; i++) {
+            if (!visited[i]) dfs(i);
+        }
+
+        Collections.sort(result);
+        StringBuilder sb = new StringBuilder();
+        sb.append(result.size()).append('\n');
+        for (int x : result) {
+            sb.append(x).append('\n');
+        }
+        System.out.print(sb);
+    }
+
+    static void dfs(int x) {
+        visited[x] = true;
+        int y = num[x];
+
+        if (!visited[y]) {
+            dfs(y);
+        } else if (!finished[y]) {
+            // 사이클이 존재할 경우
+            int cur = y;
+            do {
+                result.add(cur); // 사이클에 포함되는 노드 result에 추가
+                cur = num[cur];
+            } while (cur != y);
+        }
+
+        finished[x] = true;
+    }
+}
+```