From edb660afaebd119b4ef525b9060e6eb665c782b8 Mon Sep 17 00:00:00 2001
From: zhenxun00 <3085907783@qq.com>
Date: Mon, 17 Aug 2026 19:05:34 +0800
Subject: [PATCH 1/2] fix: add input validation to cyclic_sort (#14898)

### Describe your change:

Added input validation to cyclic_sort function to prevent infinite loops
and silent errors when the input list contains duplicates or numbers
outside the valid range.

* [ ] Add an algorithm?
* [x] Fix a bug or typo in an existing algorithm?
* [ ] Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
* [ ] Documentation change?

### Checklist:
* [x] I have read CONTRIBUTING.md.
* [x] This pull request is all my own work -- I have not plagiarized.
* [x] I know that pull requests will not be merged if they fail the automated tests.
* [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
* [x] All new Python files are placed inside an existing directory.
* [x] All filenames are in all lowercase characters with no spaces or dashes.
* [x] All functions and variable names follow Python naming conventions.
* [x] All function parameters and return values are annotated with Python type hints.
* [x] All functions have doctests that pass the automated testing.
* [ ] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
* [x] If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: Fixes #14898
---
 sorts/cyclic_sort.py | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/sorts/cyclic_sort.py b/sorts/cyclic_sort.py
index 9e81291548d4..f0aa5fb0b679 100644
--- a/sorts/cyclic_sort.py
+++ b/sorts/cyclic_sort.py
@@ -19,6 +19,8 @@ def cyclic_sort(nums: list[int]) -> list[int]:
 
     :param nums: List of n integers from 1 to n to be sorted.
     :return: The same list sorted in ascending order.
+    :raises ValueError: If input contains duplicate numbers.
+    :raises ValueError: If input contains numbers outside range 1 to n.
 
     Time complexity: O(n), where n is the number of integers in the list.
 
@@ -27,7 +29,37 @@ def cyclic_sort(nums: list[int]) -> list[int]:
     []
     >>> cyclic_sort([3, 5, 2, 1, 4])
     [1, 2, 3, 4, 5]
+    >>> cyclic_sort([1])
+    [1]
+    >>> cyclic_sort([2, 1])
+    [1, 2]
+
+    >>> cyclic_sort([7, 3, 2, 3, 54, 5, 4])
+    Traceback (most recent call last):
+        ...
+    ValueError: All numbers must be unique, got [7, 3, 2, 3, 54, 5, 4]
+
+    >>> cyclic_sort([1, 2, 5])
+    Traceback (most recent call last):
+        ...
+    ValueError: All numbers must be in range 1 to 3, got 5
     """
+    n = len(nums)
+
+    # Empty list is already sorted
+    if n == 0:
+        return nums
+
+    # Check for duplicates
+    if len(set(nums)) != n:
+        raise ValueError(f"All numbers must be unique, got {nums}")
+
+    # Check if all numbers are in range 1 to n
+    for num in nums:
+        if num < 1 or num > n:
+            raise ValueError(
+                f"All numbers must be in range 1 to {n}, got {num}"
+            )
 
     # Perform cyclic sort
     index = 0

From 5f12ba103d07df98c6b8e7a9dd2e60fab4117613 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Mon, 17 Aug 2026 18:08:38 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 sorts/cyclic_sort.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/sorts/cyclic_sort.py b/sorts/cyclic_sort.py
index f0aa5fb0b679..403e97cc50f8 100644
--- a/sorts/cyclic_sort.py
+++ b/sorts/cyclic_sort.py
@@ -57,9 +57,7 @@ def cyclic_sort(nums: list[int]) -> list[int]:
     # Check if all numbers are in range 1 to n
     for num in nums:
         if num < 1 or num > n:
-            raise ValueError(
-                f"All numbers must be in range 1 to {n}, got {num}"
-            )
+            raise ValueError(f"All numbers must be in range 1 to {n}, got {num}")
 
     # Perform cyclic sort
     index = 0