Problem 1582: Special positions in a binary matrix

problems/1582-special-positions-in-a-binary-matrix/main.rb

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+# @param {Integer[][]} mat
+# @return {Integer}
+def num_special(mat)
+  count = 0
+
+  mat.each_with_index do |row, i|
+    row.each_with_index do |cell, j|
+      count += 1 if cell == 1 && special?(mat, i, j)
+    end
+  end
+
+  count
+end
+
+def special?(mat, row_index, column_index)
+  mat[row_index].each_with_index do |cell, x|
+    return false if cell == 1 && x != column_index
+  end
+
+  mat.each_with_index do |row, x|
+    return false if row[column_index] == 1 && x != row_index
+  end
+
+  true
+end

problems/1582-special-positions-in-a-binary-matrix/readme.md

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+# 1582. Special Positions in a Binary Matrix
+
+Given an m x n binary matrix mat, return the number of special positions in mat.
+
+A position (`i`, `j`) is called special if `mat[i][j]` == `1`
+and all other elements in row `i` and column `j` are `0` (rows and columns are 0-indexed).

problems/1582-special-positions-in-a-binary-matrix/test.rb

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+require_relative 'main'
+require 'test/unit'
+
+class TestNumSpecial < Test::Unit::TestCase
+  def test_simple
+    assert_equal(1, num_special([[1, 0, 0], [0, 0, 1], [1, 0, 0]]))
+  end
+
+  def test_multiple
+    assert_equal(3, num_special([[1, 0, 0], [0, 1, 0], [0, 0, 1]]))
+  end
+end