Remove Duplicates While Preserving First-Appearance Order

Remove duplicate values from an array while preserving the order in which each distinct value first appears.

Function Contract

Implement filter_duplicates(data) -> list[int].

Return a new array containing the first occurrence of each distinct value in the input's original order.

Constraints and Clarifications

For a portable practice interface, values are integers.

• data is always an array, never null.
• 0 <= len(data) <= 200000.
• Values range from -1000000000 through 1000000000.
• Equal values count as duplicates even when separated by other values.
• Do not sort the result.
• Aim for expected O(n) time.

Examples

data = [7, 6, 4, 3, 3, 4, 9]
Output: [7, 6, 4, 3, 9]

data = [0, -1, 0, -1, 2]
Output: [0, -1, 2]