There is a city composed of n x n blocks, where each block contains a single building shaped like a vertical square prism. You are given a 0-indexed n x n integer matrix grid where grid[r][c] represents the height of the building located in the block at row r and column c.
A city's skyline is the outer contour formed by all the building when viewing the side of the city from a distance. The skyline from each cardinal direction north, east, south, and west may be different.
We are allowed to increase the height of any number of buildings by any amount (the amount can be different per building). The height of a 0-height building can also be increased. However, increasing the height of a building should not affect the city's skyline from any cardinal direction.
Return the maximum total sum that the height of the buildings can be increased by without changing the city's skyline from any cardinal direction.
Example 1:
Input: grid = [[3,0,8,4],[2,4,5,7],[9,2,6,3],[0,3,1,0]]
Output: 35
Explanation: The building heights are shown in the center of the above image.
The skylines when viewed from each cardinal direction are drawn in red.
The grid after increasing the height of buildings without affecting skylines is:
gridNew = [ [8, 4, 8, 7],
[7, 4, 7, 7],
[9, 4, 8, 7],
[3, 3, 3, 3] ]
Example 2:
Input: grid = [[0,0,0],[0,0,0],[0,0,0]] Output: 0 Explanation: Increasing the height of any building will result in the skyline changing.
Constraints:
n == grid.lengthn == grid[r].length2 <= n <= 500 <= grid[r][c] <= 100This approach involves calculating the maximum possible heights for each building in the grid so that the skyline remains unchanged. To achieve this, determine the maximum heights seen from the north/south (for each column) and from the west/east (for each row). For each building, the new maximum height is the minimum of these two values. This way, the skyline's constraints are not violated.
Once you compute the possible maximum height for each building, the sum of differences between these new heights and the original heights will yield the maximum total sum that the heights can be increased by.
This C solution first computes the maximum height seen from each row and column and stores them in two arrays, maxRow and maxCol. Then, it iterates over each building position in the grid to calculate the new possible height by taking the minimum value between the corresponding values in maxRow and maxCol. The potential increase for each building is accumulated to give the total maximum increase possible without altering the skyline.
C++
Java
Python
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Time Complexity: O(n^2) where n is the number of rows (or columns) in the grid since we must iterate over the entire grid at least twice (once for calculating maxRow and maxCol, and once for computing the total increase).
Space Complexity: O(n), as additional space for storing the skyline views of rows and columns is required.
LeetCode Max Increase to Keep City Skyline Solution Explained - Java • Nick White • 11,054 views views
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