diff --git a/solutions/double-or-one-thing/double.py b/solutions/double-or-one-thing/double.py
new file mode 100644
index 00000000..2ba29260
--- /dev/null
+++ b/solutions/double-or-one-thing/double.py
@@ -0,0 +1,61 @@
+def give_me_last_equal(string: str, position: int) -> int:
+    """
+    Given a position in a string, output the last position such as:
+    string[position] == string[position + 1] == ... == string[last_position].
+    """
+    test_letter = string[position]
+
+    last_position = position
+    while last_position < len(string) - 1 and test_letter == string[last_position + 1]:
+        last_position += 1
+
+    return last_position
+
+
+def first_alphabetically(my_str: str) -> str:
+    result = []
+
+    current = 0
+    while current < len(my_str) - 1:
+        # If the current letter comes before the next letter, highlight it.
+        if my_str[current] < my_str[current + 1]:
+            result += my_str[current] * 2
+            current += 1
+
+        # If the current letter comes after the next letter, don’t highlight it.
+        elif my_str[current] > my_str[current + 1]:
+            result += my_str[current]
+            current += 1
+
+        else:
+            # Search for the index of the first letter distinct from the
+            # current letter.
+            last_equal = give_me_last_equal(my_str, current)
+
+            # If the string ends with repeating letters, don't highlight them.
+            if last_equal == len(my_str) - 1:
+                result += my_str[current] * (last_equal - current)
+                break
+
+            # If the current letters comes before, highlight all of them.
+            elif my_str[last_equal] < my_str[last_equal + 1]:
+                result += my_str[current] * (2 * (last_equal - current + 1))
+
+            # If the current letters comes after, don't highlight them.
+            else:
+                result += my_str[current] * (last_equal - current + 1)
+
+            # Walk `last_equal - current + 1` letters forward.
+            current += last_equal - current + 1
+
+    # The last letter will never be highlighted.
+    result += my_str[-1]
+    return ''.join(result)
+    
+
+
+times = input()
+for i in range(int(times)):
+    my_string = input()
+    
+    print(f"Case #{i + 1}: {first_alphabetically(my_string)}")