Update permutations.py

data_structures/arrays/permutations.py

@@ -1,7 +1,6 @@
 def permute(nums: list[int]) -> list[list[int]]:
     """
     Return all permutations.
-
     >>> from itertools import permutations
     >>> numbers= [1,2,3]
     >>> all(list(nums) in permute(numbers) for nums in permutations(numbers))
@@ -20,7 +19,27 @@ def permute(nums: list[int]) -> list[list[int]]:
     return result
 
 
+def permute2(nums: list[int]) -> list[list[int]]:
+    def backtrack(first=0):
+        if first == n:
+            output.append(nums[:])
+        for i in range(first, n):
+            nums[first], nums[i] = nums[i], nums[first]
+            backtrack(first + 1)
+            nums[first], nums[i] = nums[i], nums[first]
+
+    n = len(nums)
+    output = []
+    backtrack()
+    return output
+
+    # return result
+
+
 if __name__ == "__main__":
     import doctest
 
+    # use res to print the data in permute2 function
+    res = permute2([1, 2, 3])
+    print(res)
     doctest.testmod()