Complete iterative solution

2 files changed, 91 insertions, 2 deletions

diff --git a/2020/08/15/README.md b/2020/08/15/README.md
index c4df310..406b6e1 100644
--- a/2020/08/15/README.md
+++ b/2020/08/15/README.md
@@ -43,5 +43,3 @@
 │print("List after reversal: ")
 │testTail.printList()
 │# 0 1 2 3 4
-
-
diff --git a/2020/08/15/main.rb b/2020/08/15/main.rb
new file mode 100644
index 0000000..2e7121d
--- /dev/null
+++ b/2020/08/15/main.rb
@@ -0,0 +1,91 @@
+def assert_equals(x, y)
+  raise [x, y].inspect unless x == y
+end
+
+class ListNode
+  attr_accessor :data, :next
+
+  def initialize(data)
+    @data = data
+    @next = nil
+  end
+
+  def to_a
+    current = self
+    items = []
+    while current
+      items << current.data
+      current = current.next
+    end
+    items
+  end
+
+  def inspect
+    print "["
+    to_a.each { |current| print "(#{current})->" }
+    puts "(nil)]"
+  end
+
+  def to_s
+    data.to_s
+  end
+end
+
+class Solution
+  def self.run(head)
+    stack = []
+    current = head
+
+    while current
+      stack.push(current)
+      current = current.next
+    end
+
+    until stack.empty?
+      c = stack.pop
+      n = stack[-1]
+      c.next = n
+    end
+  end
+end
+
+=begin
+[(4)->(3)->(2)->(1)->(0)->(nil)]
+
+list
+
+   n     c    t
+[(nil)<-(4)<-(3)<-(2)<-(1)<-(0) (nil)]
+
+# stack
+
+         c
+           n
+|0|1|2|3|4|
+
+until stack.empty?
+  c = stack.pop
+  n = stack.peek
+  t = c.next
+
+  c.next = n
+end
+
+=end
+
+head = ListNode.new(4)
+node1 = ListNode.new(3)
+node2 = ListNode.new(2)
+node3 = ListNode.new(1)
+tail = ListNode.new(0)
+
+head.next = node1
+node1.next = node2
+node2.next = node3
+node3.next = tail
+
+puts head.inspect
+assert_equals(head.to_a, [4,3,2,1,0])
+Solution.run(head)
+puts tail.inspect
+assert_equals(tail.to_a, [0,1,2,3,4])