diff --git a/lib/max_subarray.rb b/lib/max_subarray.rb index 5204edb..1618086 100644 --- a/lib/max_subarray.rb +++ b/lib/max_subarray.rb @@ -1,8 +1,26 @@ -# Time Complexity: ? -# Space Complexity: ? +# Time Complexity: O(n) because we have do our if/else operations on every element in the array +# Space Complexity: O(1) because we are re-using the same variable def max_sub_array(nums) return 0 if nums == nil - - raise NotImplementedError, "Method not implemented yet!" + return nil if nums.empty? + return nums[0] if nums.length == 1 + + max_so_far = max_ending_here = nums[0] + + nums[1..-1].each do |number| + + if max_ending_here + number < number + max_ending_here = number + else + max_ending_here += number + end + + if max_so_far < max_ending_here + max_so_far = max_ending_here + end + end + + return max_so_far + end diff --git a/lib/newman_conway.rb b/lib/newman_conway.rb index 4c985cd..403a677 100644 --- a/lib/newman_conway.rb +++ b/lib/newman_conway.rb @@ -1,7 +1,33 @@ -# Time complexity: ? -# Space Complexity: ? +# Time complexity: O(n) because we need to perform our "what is the p?" steps n times +# Space Complexity: also O(n) because we are adding an element to the sequence array for every n def newman_conway(num) - raise NotImplementedError, "newman_conway isn't implemented" + raise ArgumentError, "Argument must be an integer greater than zero." if num <= 0 + + if num == 1 + return "1" + elsif num == 2 + return "1 1" + else + p_helper(num, [1, 1]) + end +end + +def p_helper(num, sequence) + + # BASE CASE: stop when count of numbers in sequence array is the same as `num` + return sequence.join(" ") if num == sequence.length + + # REGRESSIVE CASE: add p for next integer in sequence + # forumula: p(num) = p(p(num - 1)) + p(num - p(num - 1)) + next_integer = sequence.length + 1 + # if num is 4 previous_p is at index 2 (value: 2) + previous_p = sequence[next_integer - 2] + # now we need to look up p of the previous_p value + p_previous_p = sequence[previous_p - 1] + # find p of number minus previous number's p, then add it to p_previous_p + p = p_previous_p + sequence[(next_integer - previous_p) - 1] + sequence << p + return p_helper(num, sequence) end \ No newline at end of file diff --git a/test/max_sub_array_test.rb b/test/max_sub_array_test.rb index 3253cdf..e27e1ca 100644 --- a/test/max_sub_array_test.rb +++ b/test/max_sub_array_test.rb @@ -1,6 +1,6 @@ require_relative "test_helper" -xdescribe "max subarray" do +describe "max subarray" do it "will work for [-2,1,-3,4,-1,2,1,-5,4]" do # Arrange input = [-2,1,-3,4,-1,2,1,-5,4]