diff --git a/lib/linked_list.rb b/lib/linked_list.rb index 5e173ebc..11942926 100644 --- a/lib/linked_list.rb +++ b/lib/linked_list.rb @@ -18,98 +18,201 @@ def initialize # method to add a new node with the specific data value in the linked list # insert the new node at the beginning of the linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(1) + # Space Complexity: O(1) def add_first(value) - raise NotImplementedError + new_node = Node.new(value) + new_node.next = @head + @head = new_node end # method to find if the linked list contains a node with specified value # returns true if found, false otherwise - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def search(value) - raise NotImplementedError + current = @head + until current == nil + if current.data == value + return true + else + current = current.next + end + end + return false end # method to return the max value in the linked list # returns the data value and not the node + # Time Complexity: O(n) + # Space Complexity: O(1) def find_max - raise NotImplementedError + if @head == nil + return nil + end + max_val = @head.data + current = @head + until current == nil + if current.data > max_val + max_val = current.data + end + current = current.next + end + return max_val end # method to return the min value in the linked list # returns the data value and not the node - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def find_min - raise NotImplementedError + if @head == nil + return nil + end + min_val = @head.data + current = @head + until current == nil + if current.data < min_val + min_val = current.data + end + current = current.next + end + return min_val end +#################################################################################### - # Additional Exercises + # Additional Exercises # returns the value in the first node # returns nil if the list is empty - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: 0(1) + # Space Complexity: 0(1) def get_first - raise NotImplementedError + if @head == nil + return nil + end + @head.data end # method that inserts a given value as a new last node in the linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def add_last(value) - raise NotImplementedError + if @head == nil + @head = Node.new(value) + else + current = @head + until current.next == nil + current = current.next + end + current.next = Node.new(value) + end end # method that returns the length of the singly linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: 0(n) + # Space Complexity: O(1) def length - raise NotImplementedError + count = 0 + current = @head + until current == nil + current = current.next + count += 1 + end + return count end # method that returns the value at a given index in the linked list # index count starts at 0 # returns nil if there are fewer nodes in the linked list than the index value - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def get_at_index(index) - raise NotImplementedError + count = 0 + if index > length + return nil + end + current = @head + until current == nil + if count == index + return current.data + else + count += 1 + current = current.next + end + end + return current.data end # method to print all the values in the linked list - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def visit - raise NotImplementedError + # raise NotImplementedError + current = @head + until current.next == nil + puts current.data + end end # method to delete the first node found with specified value - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def delete(value) - raise NotImplementedError + if @head == nil + return nil + end + if @head.data == value + @head = @head.next + end + current = @head + until current.next == nil + if current.next.data == value + current.next = current.next.next + end + current = current.next + end end # method to reverse the singly linked list # note: the nodes should be moved and not just the values in the nodes - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def reverse - raise NotImplementedError + previous = nil + current = @head + temp = current.next + # All variables are pointers + until current.next == nil + current.next = previous + previous = current + current = temp + temp = current.next + end + current.next = previous + @head = current + return end # method that returns the value of the last node in the linked list # returns nil if the linked list is empty - # Time Complexity: ? - # Space Complexity: ? + # Time Complexity: O(n) + # Space Complexity: O(1) def get_last - raise NotImplementedError + if @head == nil + return nil + else + current = @head + until current.next == nil + current = current.next + end + end + return current.data end - - ## Advanced Exercises + +############################################################################################################### + + ## Advanced Exercises # returns the value at the middle element in the singly linked list # Time Complexity: ? # Space Complexity: ? diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb index 77423e34..8cdc329b 100644 --- a/test/linked_list_test.rb +++ b/test/linked_list_test.rb @@ -23,7 +23,7 @@ @list.add_first(3) # Assert - expect(@list.get_at_index(0)).must_equal 3 + expect(@list.get_first()).must_equal 3 end it 'will put the last added item to the front of the list' do @@ -32,18 +32,18 @@ @list.add_first(2) # Assert - expect(@list.get_at_index(0)).must_equal 2 + expect(@list.get_first()).must_equal 2 # Act again @list.add_first(3) # Assert - expect(@list.get_at_index(0)).must_equal 3 + expect(@list.get_first()).must_equal 3 end it 'will return `nil` for `getFirst` if the list is empty' do - expect(@list.get_at_index(0)).must_be_nil + expect(@list.get_first()).must_be_nil end end @@ -59,10 +59,10 @@ end it "returns false if the element is not in the list" do - @list = LinkedList.new - @list.add_first(3) - @list.add_first(2) - expect(@list.search("pasta")).must_equal false + @list = LinkedList.new + @list.add_first(3) + @list.add_first(2) + expect(@list.search("pasta")).must_equal false end it "returns false for an empty list" do @@ -103,7 +103,7 @@ end end - xdescribe "Optional addLast & getLast" do + describe "Optional addLast & getLast" do it "will add to the front if the list is empty" do @list.add_last(1) expect(@list.get_at_index(0)).must_equal 1