From dc3095d3ce47d62bf1bced19e00efe9a501dc3ec Mon Sep 17 00:00:00 2001
From: jeeminimini <jiminn821@naver.com>
Date: Mon, 20 Nov 2023 20:37:52 +0900
Subject: [PATCH] =?UTF-8?q?feat=20:=20=EC=88=AB=EC=9E=90=EA=B3=A0=EB=A5=B4?=
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---
 ...20\352\263\240\353\245\264\352\270\260.py" | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 "src/main/kotlin/jimin/50week/\354\210\253\354\236\220\352\263\240\353\245\264\352\270\260.py"

diff --git "a/src/main/kotlin/jimin/50week/\354\210\253\354\236\220\352\263\240\353\245\264\352\270\260.py" "b/src/main/kotlin/jimin/50week/\354\210\253\354\236\220\352\263\240\353\245\264\352\270\260.py"
new file mode 100644
index 00000000..6776da1a
--- /dev/null
+++ "b/src/main/kotlin/jimin/50week/\354\210\253\354\236\220\352\263\240\353\245\264\352\270\260.py"
@@ -0,0 +1,36 @@
+'''
+처음에는 그냥 dfs로 했더니 시간초과났다
+
+사이클을 도는 친구를 찾아야한다..
+https://velog.io/@deannn/BOJ-%EB%B0%B1%EC%A4%80-2668%EB%B2%88-%EC%88%AB%EC%9E%90%EA%B3%A0%EB%A5%B4%EA%B8%B0-Python
+참고
+'''
+
+import sys
+n = int(sys.stdin.readline())
+numbers = [0]
+for i in range(n):
+    numbers.append(int(sys.stdin.readline()))
+
+answer = set()
+
+
+def dfs(first, second, now):
+    first.add(now)
+    second.add(numbers[now])
+    if numbers[now] in first:
+        if first == second:
+            answer.update(first)
+            return
+        return
+    return dfs(first, second, numbers[now])
+
+
+for i in range(1, n + 1):
+    if i not in answer:
+        dfs(set(), set(), i)
+
+print(len(answer))
+for num in sorted(list(answer)):
+    print(num)
+