feat: Add the section of permutations problem. (#476)

* Add the section of permutations problem.

* Update permutations_problem.md

codes/python/chapter_array_and_linkedlist/array.py

@@ -54,6 +54,9 @@ def traverse(nums: list[int]) -> None:
     # 直接遍历数组
     for num in nums:
         count += 1
+    # 同时遍历数据索引和元素
+    for i, num in enumerate(nums):
+        count += 1
 
 
 def find(nums: list[int], target: int) -> int: