Pascals Triangle

practice/pascals-triangle/pascals_triangle.py

@@ -1,2 +1,38 @@
 def rows(row_count):
-    pass
+    """
+    Generate the first `row_count` rows of Pascal's Triangle.
+
+    Pascal's Triangle is a triangle of numbers where each number is the sum of
+    the two numbers directly above it. The triangle starts with a single 1 at
+    the top, and each row has one more element than the previous row.
+
+    Args:
+        row_count (int): The number of rows to generate.
+
+    Returns:
+        list: A list of lists representing the first `row_count` rows of Pascal's Triangle.
+
+    Raises:
+        ValueError: If `row_count` is negative.
+
+    Examples:
+        >>> rows(3)
+        [[1], [1, 1], [1, 2, 1]]
+    """
+    if row_count < 0:
+        raise ValueError("number of rows is negative")
+    elif row_count == 0:
+        return []
+    elif row_count == 1:
+        return [[1]]
+    else:
+        # Generate the first `row_count - 1` rows
+        triangle = rows(row_count - 1)
+
+        # Calculate the new row based on the last row
+        last_row = triangle[-1]
+        new_row = [1] + [last_row[i] + last_row[i+1] for i in range(len(last_row) - 1)] + [1]
+
+        # Append the new row to the triangle and return it
+        triangle.append(new_row)
+        return triangle