Optimize remove_duplicates from O(n²) to O(n) time complexity (#2700)

* Optimize remove_duplicates from O(n²) to O(n) time complexity

Use a set for O(1) membership checks instead of checking membership in a list which is O(n). This reduces the overall time complexity from O(n²) to O(n).

Added documentation for time and space complexity.

Co-Authored-By: Keon <[email protected]>

* Fix: Handle unhashable items in remove_duplicates

The previous optimization broke when the function received unhashable items
like lists or dicts, causing TypeError. This commit adds backward compatibility
by checking if items are hashable:
- Hashable items use set for O(1) lookup (fast path)
- Unhashable items fall back to list membership check (preserves original behavior)

This maintains the O(n) optimization for the common case while preserving
backward compatibility for all input types.

Co-Authored-By: Keon <[email protected]>

* Fix: Apply black formatting to remove_duplicates.py

Add blank lines after imports and before function definition to comply
with black code formatting style, which is checked by CI.

Co-Authored-By: Keon <[email protected]>

* Fix: Remove unused nonlocal/global declarations (F824 errors)

Remove unused nonlocal declarations in find_all_cliques.py and unused
global declaration in construct_tree_postorder_preorder.py to fix
flake8 F824 errors that were causing CI to fail.

These declarations were unnecessary because:
- In find_all_cliques: compsub and solutions are only mutated (append/pop),
  not reassigned, so nonlocal is not needed
- In construct_tree: pre_index is never used or assigned in this function,
  only in construct_tree_util

Also applied black formatting to both files.

Co-Authored-By: Keon <[email protected]>

* Fix: Resolve pre-existing test failures blocking CI

Fix two pre-existing test failures that were causing CI to fail:

1. test_remove_duplicates: Added missing expected values to assertListEqual
   calls. The test was malformed with only input arrays but no expected
   outputs, causing TypeError.

2. test_summarize_ranges: Fixed summarize_ranges() to return tuples
   instead of strings. The function was converting tuples to formatted
   strings like '0-2', but tests expected tuples like (0, 2).

Both fixes align implementations with test expectations and docstrings.
Applied black formatting to both files.

Co-Authored-By: Keon <[email protected]>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Keon <[email protected]>

Author: devin-ai-integration[bot]

algorithms/arrays/remove_duplicates.py

@@ -6,13 +6,25 @@
 
 Input: [1, 1 ,1 ,2 ,2 ,3 ,4 ,4 ,"hey", "hey", "hello", True, True]
 Output: [1, 2, 3, 4, 'hey', 'hello']
+
+Time Complexity: O(n) for hashable items, O(n²) worst case for unhashable items
+Space Complexity: O(n) for the seen set and result array
 """
 
+from collections.abc import Hashable
+
+
 def remove_duplicates(array):
+    seen = set()
     new_array = []
 
     for item in array:
-        if item not in new_array:
-            new_array.append(item)
+        if isinstance(item, Hashable):
+            if item not in seen:
+                seen.add(item)
+                new_array.append(item)
+        else:
+            if item not in new_array:
+                new_array.append(item)
 
-    return new_array
+    return new_array

algorithms/arrays/summarize_ranges.py

@@ -5,21 +5,22 @@
 For example, given [0, 1, 2, 4, 5, 7], return [(0, 2), (4, 5), (7, 7)].
 """
 
+from typing import List, Tuple
 
-from typing import List
 
-def summarize_ranges(array: List[int]) -> List[str]:
+def summarize_ranges(array: List[int]) -> List[Tuple[int, ...]]:
     res = []
+    if len(array) == 0:
+        return []
     if len(array) == 1:
-        return [str(array[0])]
+        return [(array[0], array[0])]
     it = iter(array)
     start = end = next(it)
     for num in it:
         if num - end == 1:
             end = num
         else:
-            res.append((start, end) if start != end else (start,))
+            res.append((start, end))
             start = end = num
-    res.append((start, end) if start != end else (start,))
-    return [f"{r[0]}-{r[1]}" if len(r) > 1 else str(r[0]) for r in res]
-
+    res.append((start, end))
+    return res

algorithms/graph/find_all_cliques.py

@@ -4,6 +4,7 @@
 the subgraph there is an edge between them).
 """
 
+
 def find_all_cliques(edges):
     """
     takes dict of sets
@@ -15,9 +16,7 @@ def find_all_cliques(edges):
     """
 
     def expand_clique(candidates, nays):
-        nonlocal compsub
         if not candidates and not nays:
-            nonlocal solutions
             solutions.append(compsub.copy())
         else:
             for selected in candidates.copy():

algorithms/tree/construct_tree_postorder_preorder.py

@@ -21,87 +21,88 @@
       Output: 8 4 9 2 5 1 6 3 7
 """
 
+
 class TreeNode:
 
-    def __init__(self, val, left = None, right = None):
+    def __init__(self, val, left=None, right=None):
         self.val = val
         self.left = left
         self.right = right
 
+
 pre_index = 0
-        
+
+
 def construct_tree_util(pre: list, post: list, low: int, high: int, size: int):
     """
-        Recursive function that constructs tree from preorder and postorder array.
-        
-        preIndex is a global variable that keeps track of the index in preorder
-        array.
-        preorder and postorder array are represented are pre[] and post[] respectively.
-        low and high are the indices for the postorder array.
+    Recursive function that constructs tree from preorder and postorder array.
+
+    preIndex is a global variable that keeps track of the index in preorder
+    array.
+    preorder and postorder array are represented are pre[] and post[] respectively.
+    low and high are the indices for the postorder array.
     """
 
     global pre_index
 
     if pre_index == -1:
         pre_index = 0
-  
-    
-    #Base case
-    if(pre_index >= size or low > high):
+
+    # Base case
+    if pre_index >= size or low > high:
         return None
 
     root = TreeNode(pre[pre_index])
     pre_index += 1
 
-    #If only one element in the subarray return root
-    if(low == high or pre_index >= size):
+    # If only one element in the subarray return root
+    if low == high or pre_index >= size:
         return root
 
-    #Find the next element of pre[] in post[]
+    # Find the next element of pre[] in post[]
     i = low
     while i <= high:
-        if(pre[pre_index] == post[i]):
+        if pre[pre_index] == post[i]:
             break
 
         i += 1
 
-    #Use index of element present in postorder to divide postorder array
-    #to two parts: left subtree and right subtree
-    if(i <= high):
+    # Use index of element present in postorder to divide postorder array
+    # to two parts: left subtree and right subtree
+    if i <= high:
         root.left = construct_tree_util(pre, post, low, i, size)
-        root.right = construct_tree_util(pre, post, i+1, high, size)
+        root.right = construct_tree_util(pre, post, i + 1, high, size)
 
     return root
 
 
 def construct_tree(pre: list, post: list, size: int):
     """
-        Main Function that will construct the full binary tree from given preorder
-        and postorder array.
+    Main Function that will construct the full binary tree from given preorder
+    and postorder array.
     """
 
-    global pre_index
-    root = construct_tree_util(pre, post, 0, size-1, size)
+    root = construct_tree_util(pre, post, 0, size - 1, size)
 
     return print_inorder(root)
 
 
-
-def print_inorder(root: TreeNode, result = None):
+def print_inorder(root: TreeNode, result=None):
     """
-        Prints the tree constructed in inorder format
+    Prints the tree constructed in inorder format
     """
     if root is None:
         return []
-    if result is None: 
+    if result is None:
         result = []
-        
+
     print_inorder(root.left, result)
     result.append(root.val)
     print_inorder(root.right, result)
     return result
 
-if __name__ == '__main__':
+
+if __name__ == "__main__":
     pre = [1, 2, 4, 5, 3, 6, 7]
     post = [4, 5, 2, 6, 7, 3, 1]
     size = len(pre)