2352-equal-row-and-column-pairs.rb

# frozen_string_literal: true

# 2352. Equal Row and Column Pairs
# https://leetcode.com/problems/equal-row-and-column-pairs
# Medium

=begin
Given a 0-indexed n x n integer matrix grid, return the number of pairs (ri, cj) such that row ri and column cj are equal.

A row and column pair is considered equal if they contain the same elements in the same order (i.e., an equal array).

Example 1:
Input: grid = [[3,2,1],[1,7,6],[2,7,7]]
Output: 1
Explanation: There is 1 equal row and column pair:
- (Row 2, Column 1): [2,7,7]

Example 2:
Input: grid = [[3,1,2,2],[1,4,4,5],[2,4,2,2],[2,4,2,2]]
Output: 3
Explanation: There are 3 equal row and column pairs:
- (Row 0, Column 0): [3,1,2,2]
- (Row 2, Column 2): [2,4,2,2]
- (Row 3, Column 2): [2,4,2,2]

Constraints:
n == grid.length == grid[i].length
1 <= n <= 200
1 <= grid[i][j] <= 105
=end

# @param {Integer[][]} grid
# @return {Integer}
def equal_pairs(grid)
  row_counts = Hash.new(0)
  col_counts = Hash.new(0)
  result = 0
  grid.each { |el| row_counts[el] += 1 }
  grid.size.times { |i| col_counts[grid.map { |el| el[i - 1] }] += 1 }

  row_counts.each do |key, value|
    if !col_counts[key].nil?
      result += value * col_counts[key]
    end
  end
  result
end

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

require "test/unit"
class Test_equal_pairs < Test::Unit::TestCase
  def test_
    assert_equal 1, equal_pairs([[3, 2, 1], [1, 7, 6], [2, 7, 7]])
    assert_equal 3, equal_pairs([[3, 1, 2, 2], [1, 4, 4, 5], [2, 4, 2, 2], [2, 4, 2, 2]])
  end
end