Problem

At DoorDash, you are given GPS points for a delivery region. Implement a function that returns the convex hull boundary of these points, including all points that lie on the boundary edges (not just the corner vertices).

Formal Specification

• Input: points: list[list[int]] where each point is [x, y] (may contain duplicates).
• Output: list[list[int]] of unique boundary points in counterclockwise (CCW) order, starting from the leftmost-lowest point.

A point must be included if it lies on the perimeter of the convex hull (including collinear points along edges). Points strictly inside the hull must be excluded.

Examples

Example 1

• Input: points = [[0,0],[1,1],[2,2],[2,0],[2,4],[3,3],[4,2]]
• Output: [[0,0],[2,0],[4,2],[2,4]]
• Explanation: The hull corners are (0,0),(2,0),(4,2),(2,4); (1,1),(2,2),(3,3) are inside.

Example 2

• Input: points = [[0,0],[1,0],[2,0],[3,0]]
• Output: [[0,0],[1,0],[2,0],[3,0]]
• Explanation: All points are collinear and lie on the hull boundary, so all are returned.

Constraints

• 1 <= len(points) <= 10^4
• -10^9 <= x, y <= 10^9
• points may contain duplicates
• Return unique boundary points in CCW order starting from the leftmost-lowest point