Commit 483474a

@@ -0,0 +1,102 @@
+<<-DOC
+Note: Try to solve this task in O(n) time using O(1) additional space, where n is the number of elements in the list, since this is what you'll be asked to do during an interview.
+
+Given a singly linked list of integers l and an integer k, remove all elements from list l that have a value equal to k.
+
+Example
+
+For l = [3, 1, 2, 3, 4, 5] and k = 3, the output should be
+removeKFromList(l, k) = [1, 2, 4, 5];
+For l = [1, 2, 3, 4, 5, 6, 7] and k = 10, the output should be
+removeKFromList(l, k) = [1, 2, 3, 4, 5, 6, 7].
+Input/Output
+
+[time limit] 4000ms (rb)
+[input] linkedlist.integer l
+
+A singly linked list of integers.
+
+Guaranteed constraints:
+0 ≤ list size ≤ 105,
+-1000 ≤ element value ≤ 1000.
+
+[input] integer k
+
+An integer.
+
+Guaranteed constraints:
+-1000 ≤ k ≤ 1000.
+
+[output] linkedlist.integer
+
+Return l with all the values equal to k removed.
+DOC
+
+describe "remove_k_from_list" do
+  def remove_k_from_list(head, target)
+    current = head
+    previous = nil
+
+    until current.nil?
+      if current.value == target
+        if previous.nil?
+          head = current.next
+          current = head
+        else
+          previous.next = current.next
+          current = current.next
+        end
+      else
+        previous = current
+        current = current.next
+      end
+    end
+    head
+  end
+
+  class ListNode
+    attr_accessor :value, :next
+
+    def initialize(value, next_node: nil)
+      @value = value
+      @next = next_node
+    end
+
+    def to_a
+      result = []
+      current = self
+      until current.nil?
+        result.push(current.value)
+        current = current.next
+      end
+      result
+    end
+  end
+
+  def to_list(items)
+    x = nil
+    items.inject(nil) do |memo, item|
+      node = ListNode.new(item)
+      if memo.nil?
+        x = node
+      else
+        memo.next = node
+      end
+      node
+    end
+    x
+  end
+
+  [
+    { l: [3, 1, 2, 3, 4, 5], k: 3, x: [1, 2, 4, 5] },
+    { l: [1, 2, 3, 4, 5, 6, 7], k: 10, x: [1, 2, 3, 4, 5, 6, 7] },
+    { l: [1000, 1000], k: 1000, x: [] },
+    { l: [], k: -1000, x: [] },
+    { l: [123, 456, 789, 0], k: 0, x: [123, 456, 789] },
+  ].each do |x|
+    it do
+      list = to_list(x[:l])
+      expect(remove_k_from_list(list, x[:k]).to_a).to eql(x[:x])
+    end
+  end
+end