fixed the issue in strings/join.py (TheAlgorithms#12434)

* fixed the issue in strings/join.py

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* Update join.py

* Update join.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Maxim Smolskiy <[email protected]>

Author: 3 people

strings/join.py

@@ -24,6 +24,8 @@ def join(separator: str, separated: list[str]) -> str:
     'a'
     >>> join(" ", ["You", "are", "amazing!"])
     'You are amazing!'
+    >>> join(",", ["", "", ""])
+    ',,'
 
     This example should raise an
     exception for non-string elements:
@@ -37,15 +39,33 @@ def join(separator: str, separated: list[str]) -> str:
     'apple-banana-cherry'
     """
 
-    joined = ""
+    # Check that all elements are strings
     for word_or_phrase in separated:
+        # If the element is not a string, raise an exception
         if not isinstance(word_or_phrase, str):
             raise Exception("join() accepts only strings")
+
+    joined: str = ""
+    """
+    The last element of the list is not followed by the separator.
+    So, we need to iterate through the list and join each element
+    with the separator except the last element.
+    """
+    last_index: int = len(separated) - 1
+    """
+    Iterate through the list and join each element with the separator.
+    Except the last element, all other elements are followed by the separator.
+    """
+    for word_or_phrase in separated[:last_index]:
+        # join the element with the separator.
         joined += word_or_phrase + separator
 
-    # Remove the trailing separator
-    # by stripping it from the result
-    return joined.strip(separator)
+    # If the list is not empty, join the last element.
+    if separated != []:
+        joined += separated[last_index]
+
+    # Return the joined string.
+    return joined
 
 
 if __name__ == "__main__":