1975-maximum-matrix-sum.rb

# frozen_string_literal: true

# 1975. Maximum Matrix Sum
# https://leetcode.com/problems/maximum-matrix-sum
# Medium

=begin
You are given an n x n integer matrix. You can do the following operation any number of times:
* Choose any two adjacent elements of matrix and multiply each of them by -1.
Two elements are considered adjacent if and only if they share a border.
Your goal is to maximize the summation of the matrix's elements. Return the maximum sum of the matrix's elements using the operation mentioned above.

Example 1:
Input: matrix = [[1,-1],[-1,1]]
Output: 4
Explanation: We can follow the following steps to reach sum equals 4:
- Multiply the 2 elements in the first row by -1.
- Multiply the 2 elements in the first column by -1.

Example 2:
Input: matrix = [[1,2,3],[-1,-2,-3],[1,2,3]]
Output: 16
Explanation: We can follow the following step to reach sum equals 16:
- Multiply the 2 last elements in the second row by -1.

Constraints:
* n == matrix.length == matrix[i].length
* 2 <= n <= 250
* -10^5 <= matrix[i][j] <= 10^5
=end

# @param {Integer[][]} matrix
# @return {Integer}
def max_matrix_sum(matrix)
  m = matrix.flatten!
  m.count { 0 > _1 } % 2 * 2 * -m.map!(&:abs).min + m.sum
end

# **************** #
#       TEST       #
# **************** #

require "test/unit"
class Test_max_matrix_sum < Test::Unit::TestCase
  def test_
    assert_equal(4, max_matrix_sum([[1, -1], [-1, 1]]))
    assert_equal(16, max_matrix_sum([[1, 2, 3], [-1, -2, -3], [1, 2, 3]]))
  end
end