You are given a positive integer n, representing an n x n city. You are also given a 2D grid buildings, where buildings[i] = [x, y] denotes a unique building located at coordinates [x, y].
A building is covered if there is at least one building in all four directions: left, right, above, and below.
Return the number of covered buildings.
Example 1:
Input: n = 3, buildings = [[1,2],[2,2],[3,2],[2,1],[2,3]]
Output: 1
Explanation:
[2,2] is covered as it has at least one building:
[1,2])[3,2])[2,1])[2,3])Example 2:
Input: n = 3, buildings = [[1,1],[1,2],[2,1],[2,2]]
Output: 0
Explanation:
Example 3:
Input: n = 5, buildings = [[1,3],[3,2],[3,3],[3,5],[5,3]]
Output: 1
Explanation:
[3,3] is covered as it has at least one building:
[1,3])[5,3])[3,2])[3,5])
Constraints:
2 <= n <= 1051 <= buildings.length <= 105 buildings[i] = [x, y]1 <= x, y <= nbuildings are unique.