Refactor merge_intervals function docstring

Updated docstring formatting and improved error message clarity.

Author: gokul000410

data_structures/arrays/merge_intervals.py

@@ -1,5 +1,5 @@
 def merge_intervals(intervals: list[list[int]]) -> list[list[int]]:
-   """
+    """
     Merge all overlapping intervals.
 
     Each interval is represented as a list of two integers [start, end].
@@ -17,7 +17,8 @@ def merge_intervals(intervals: list[list[int]]) -> list[list[int]]:
     - Single interval: returns the interval itself
     - Intervals already sorted or unsorted
     - Fully overlapping intervals
-    - Invalid intervals (e.g., [[]] or intervals not having exactly 2 integers) raise ValueError
+    - Invalid intervals (e.g., [[]] or intervals not having exactly
+      2 integers) raise ValueError
 
     Examples:
     >>> merge_intervals([[1, 3], [2, 6], [8, 10], [15, 18]])
@@ -40,10 +41,12 @@ def merge_intervals(intervals: list[list[int]]) -> list[list[int]]:
 
     if not intervals:
         return []
+
     for interval in intervals:
         msg = f"Each interval must have exactly 2 integers, got {interval}"
         if len(interval) != 2:
             raise ValueError(msg)
+
     # Sort intervals based on the start time
     intervals.sort(key=lambda interval: interval[0])
 
@@ -59,3 +62,4 @@ def merge_intervals(intervals: list[list[int]]) -> list[list[int]]:
             merged.append(current)
 
     return merged
+