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3531. Count Covered Buildings

Description

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:

  • Only building [2,2] is covered as it has at least one building:
    • above ([1,2])
    • below ([3,2])
    • left ([2,1])
    • right ([2,3])
  • Thus, the count of covered buildings is 1.

Example 2:

Input: n = 3, buildings = [[1,1],[1,2],[2,1],[2,2]]

Output: 0

Explanation:

  • No building has at least one building in all four directions.

Example 3:

Input: n = 5, buildings = [[1,3],[3,2],[3,3],[3,5],[5,3]]

Output: 1

Explanation:

  • Only building [3,3] is covered as it has at least one building:
    • above ([1,3])
    • below ([5,3])
    • left ([3,2])
    • right ([3,5])
  • Thus, the count of covered buildings is 1.

 

Constraints:

  • 2 <= n <= 105
  • 1 <= buildings.length <= 105
  • buildings[i] = [x, y]
  • 1 <= x, y <= n
  • All coordinates of buildings are unique.

Solutions

Solution 1

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