From 80826a9213b49ec029bbd8d5cb07814f01bd825b Mon Sep 17 00:00:00 2001
From: alator-ux <vavilkin.max@mail.ru>
Date: Sun, 31 Oct 2021 20:05:16 +0300
Subject: [PATCH] added kruskal algorithm for matrix based graph

---
 lib/visual_graphs.rb                    |  1 +
 lib/visual_graphs/algorithms/Kruskal.rb | 73 +++++++++++++++++++++++++
 test/algorithms/kruskal_amb_test.rb     | 58 ++++++++++++++++++++
 3 files changed, 132 insertions(+)
 create mode 100644 lib/visual_graphs/algorithms/Kruskal.rb
 create mode 100644 test/algorithms/kruskal_amb_test.rb

diff --git a/lib/visual_graphs.rb b/lib/visual_graphs.rb
index de0013e..ad7ad34 100644
--- a/lib/visual_graphs.rb
+++ b/lib/visual_graphs.rb
@@ -2,6 +2,7 @@
 
 require_relative "visual_graphs/version"
 require_relative "visual_graphs/graph"
+require_relative 'visual_graphs/algorithms/Kruskal'
 module VisualGraphs
   class Error < StandardError; end
 end
diff --git a/lib/visual_graphs/algorithms/Kruskal.rb b/lib/visual_graphs/algorithms/Kruskal.rb
new file mode 100644
index 0000000..144593c
--- /dev/null
+++ b/lib/visual_graphs/algorithms/Kruskal.rb
@@ -0,0 +1,73 @@
+require 'matrix'
+
+class Kruskal_Helper
+  attr_reader :parent, :result
+
+  def initialize(size)
+    @parent = Array.new(size) {|i| i}
+    @result = Array.new(size) { |i| Array.new(size) { |j| i == j ? 0 : -1} } # временная замена, т.к. нет нужного класса
+  end
+
+
+  def find(i)
+    while i != @parent[i]
+      i = @parent[i]
+    end
+    return i
+  end
+
+  def union(i, j, w)
+    a = find(i)
+    b = find(j)
+    @parent[a] = b
+    addEdge(i,j,w)
+  end
+
+  def addEdge(first, second, weight)
+    @result[first][second] = weight
+    @result[second][first] = weight
+  end
+
+  def result
+    return @result
+  end
+end
+
+def kruskal(matrix)
+  exists = lambda do |weight|
+    weight > 0
+  end
+
+  # следующие три строки честно взяты из интернета, я их не понимаю
+  n_bytes = [42].pack('i').size
+  n_bits = n_bytes * 16
+  max_integer = 2 ** (n_bits - 2) - 1
+
+  sz = matrix[0].size
+  helper = Kruskal_Helper.new sz
+
+  (0...matrix.size - 1).each {
+    min = max_integer
+    a = -1
+    b = -1
+
+    (0...sz).each do |i|
+      (0...sz).each do |j|
+        way = matrix[i][j]
+        if exists.call(way)
+          if helper.find(i) != helper.find(j) and way < min
+            min = way
+            a = i
+            b = j
+          end
+        end
+      end
+    end
+
+    helper.union a, b, min
+  }
+
+  #p matrix
+  #p helper.result
+  helper.result
+end
diff --git a/test/algorithms/kruskal_amb_test.rb b/test/algorithms/kruskal_amb_test.rb
new file mode 100644
index 0000000..126f145
--- /dev/null
+++ b/test/algorithms/kruskal_amb_test.rb
@@ -0,0 +1,58 @@
+require 'minitest/autorun'
+require "visual_graphs"
+#Test for Kruskal's algorithm for adjacency matrix based graph
+class Kruskal_ambTest < Minitest::Test
+  include VisualGraphs
+  def setup
+    # Do nothing
+  end
+
+  def teardown
+    # Do nothing
+  end
+
+  def test1
+    matrix =
+      [
+        [0, 7, 8, -1, -1,-1],
+        [7, 0, 11, 2, -1, -1],
+        [8, 11, 0, 6, 9, -1],
+        [-1, 2, 6, 0, 11, 9],
+        [-1, -1, 9, 11, 0, 10],
+        [-1, -1, -1, 9, 10, 0]
+      ]
+    expected =
+    [
+      [0,7,-1,-1,-1,-1],
+      [7,0,-1,2,-1,-1],
+      [-1,-1,0,6,9,-1],
+      [-1,2,6,0,-1,9],
+      [-1,-1,9,-1,0,-1],
+      [-1,-1,-1,9,-1,0]
+    ]
+    result = kruskal matrix
+    assert_equal result, expected
+  end
+
+  def test2
+    matrix =
+    [
+      [0,2,-1,6,-1],
+      [2,0,3,8,5],
+      [-1,3,0,-1,7],
+      [6,8,-1,0,9],
+      [-1,5,7,9,0]
+    ]
+    expected =
+    [
+      [0,2,-1,6,-1],
+      [2,0,3,-1,5],
+      [-1,3,0,-1,-1],
+      [6,-1,-1,0,-1],
+      [-1,5,-1,-1,0],
+    ]
+    result = kruskal matrix
+    assert_equal result, expected
+  end
+
+end
\ No newline at end of file