Merge pull request #63 from MIT-Emerging-Talent/54-maximum-length-of-…

…a-concatenated-string-with-unique-characters

upload maximum_length.py challenge

solutions/maximum_length.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+A module to find the maximum length of the
+concatenation of a subsequence of arr that has unique characters.
+
+Return the maximum possible length of s
+
+Module contents:
+    - maxLength: Function to get the Maximum Length of a Concatenated String with Unique Characters
+    - backtrack: Helper function to perform backtracking
+
+Created on 2024-01-12
+Author: Kefah Albashityalshaer
+"""
+
+
+def max_length(arr: list) -> int:
+    """
+    Function to get the Maximum Length of a Concatenated String with Unique Characters
+
+    Takes a list of strings and returns the max length of concatenated string with unique characters
+
+    Parameters:
+        arr: list of stings elements to process
+
+    Returns -> int: the maximum length
+
+    Examples:
+    >>> max_length(["un","iq","ue"])
+    4
+    >>> max_length(["cha","r","act","ers"])
+    6
+    >>> max_length(["abcdefghijklmnopqrstuvwxyz"])
+    26
+    >>> max_length(["a", "bb", "ccc"])
+    1
+    >>> max_length([])
+    0
+    """
+    assert isinstance(arr, list), "input should be a list of strings"
+
+    # Helper function to perform backtracking
+    def backtrack(index, current_string):
+        # If the current string has duplicate characters, return 0
+        if len(current_string) != len(set(current_string)):
+            return 0
+
+        # Calculate the maximum length by trying to add each subsequent string
+        max_length = len(current_string)
+        for i in range(index, len(arr)):
+            max_length = max(max_length, backtrack(i + 1, current_string + arr[i]))
+        return max_length
+
+    # Start the backtracking from index 0 and an empty string
+    return backtrack(0, "")

solutions/tests/test_maximum_length.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+Test module for maximum_length function.
+
+Test categories:
+    - Standard cases: list of strings that may have unique or overlapping characters
+    - Edge cases: empty lists, strings with identical bounds or duplicate characters, substrings with repetitive letters
+    - Defensive tests: invalid inputs, assertions, or `TypeError` exceptions
+
+Created on 2024-01-12
+Author: Kefah Albashityalshaer
+"""
+
+import unittest
+
+from ..maximum_length import max_length
+
+
+class TestMaxLengthFunction(unittest.TestCase):
+    # Standard test cases
+    def test_basic_cases(self):
+        self.assertEqual(
+            max_length(["un", "iq", "ue"]), 4
+        )  # "uniq" forms a concatenated string of length 4
+        self.assertEqual(
+            max_length(["cha", "r", "act", "ers"]), 6
+        )  # The longest concatenated string is "acters" (length 6)
+        self.assertEqual(
+            max_length(["abcdefghijklmnopqrstuvwxyz"]), 26
+        )  # The string contains all unique lowercase letters (length 26)
+
+    # Edge Cases
+    def test_empty_list(self):
+        self.assertEqual(
+            max_length([]), 0
+        )  # No strings to concatenate, so the result is 0
+
+    def test_single_element(self):
+        self.assertEqual(max_length(["a"]), 1)
+        self.assertEqual(max_length(["abcdef"]), 6)
+
+    def test_no_unique_concatenation(self):
+        self.assertEqual(max_length(["a", "bb", "ccc"]), 1)
+
+    def test_repeated_characters(self):
+        self.assertEqual(max_length(["abc", "def", "abc"]), 6)
+
+    def test_large_input(self):
+        arr = ["ab", "cd", "ef", "gh", "ij", "kl", "mnop"]
+        self.assertEqual(max_length(arr), 16)  # Longest possible combination
+
+    # Defensive tests
+    def test_invalid_input(self):
+        with self.assertRaises(
+            AssertionError,
+            msg="Input should raise an AssertionError for non-list input.",
+        ):
+            max_length("not a list")
+
+    def test_non_string_input(self):
+        with self.assertRaises(TypeError):
+            max_length(["abc", 123, "def"])
+
+    def test_empty_strings(self):
+        self.assertEqual(max_length(["", "abc", "de"]), 5)
+
+
+if __name__ == "__main__":
+    unittest.main()