Given a list of buildings [left, right, height], return the key points of the skyline.
Example 1
Input: buildings = [[2,9,10]]
Output: [[2,10],[9,0]]
Explanation: One building defines two key points.
Output: [[2,10],[9,0]]
Explanation: One building defines two key points.
Example 2
Input: buildings = [[0,2,3],[2,5,3]]
Output: [[0,3],[5,0]]
Explanation: Two buildings of the same height.
Output: [[0,3],[5,0]]
Explanation: Two buildings of the same height.