exercism 77 Simple linked List

Author: kumar91gopi

README.md

@@ -298,6 +298,7 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 74. [Atbash Cipher](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/atbash_cipher.rb)
 75. [Crypto Square](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/crypto_square.rb)
 76. [List Ops](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/list_ops.rb)
+77. [Simple Linked List](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/exercism/simple_linked_list.rb)
 
 <a name="leetcode"/>
 

exercism/simple_linked_list.rb

@@ -0,0 +1,71 @@
+# Problem : https://exercism.org/tracks/ruby/exercises/simple-linked-list
+
+# Solution
+class Element
+    attr_accessor :next,:datum
+    def initialize(data)
+      @datum = data
+      @next = nil
+    end
+end
+
+class SimpleLinkedList
+    def initialize(elements=[])
+      @head = nil
+      elements.each do |element|
+        push(Element.new(element))
+      end
+    end
+
+    def push(element)
+      if @head.nil?
+        @head = element
+      else
+        tail = find_tail
+        tail.next = element
+      end
+      self
+    end
+
+    def pop
+      current = @head
+      if @head.nil? or @head.next.nil?
+        @head = nil
+        return current
+      end
+      current = current.next until current.next.next.nil?
+      last_node = current.next
+      current.next = nil
+      last_node
+    end
+
+    def to_a
+      current = @head
+      data = []
+      until current.nil?
+        data.push(current.datum)
+        current = current.next
+      end
+      data.reverse
+    end
+
+    def reverse!
+      current = @head
+      prev = nil
+      until current.nil?
+        next_node = current.next
+        current.next = prev
+        prev = current
+        current = next_node
+      end
+      @head = prev
+      self
+    end
+
+    private
+    def find_tail
+      node = @head
+      node = node.next until node.next.nil?
+      node
+    end
+end