Amy W

lib/max_subarray.rb

@@ -1,8 +1,16 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n) where n is the value of nums
+# Space Complexity: O(1)
 def max_sub_array(nums)
-    return 0 if nums == nil
-
-    raise NotImplementedError, "Method not implemented yet!"
+  return 0 if nums == nil
+
+  max_so_far = nil
+  max_ending_here = 0
+
+  nums.each do |num|
+    max_ending_here = max_ending_here + num
+    max_so_far = max_ending_here if !max_so_far || max_ending_here > max_so_far
+    max_ending_here = 0 if max_ending_here < 0
+  end
+  return max_so_far
 end

lib/newman_conway.rb

@@ -1,7 +1,21 @@
+# Time complexity: O(n) where n is the value of num
+# Space Complexity: O(n) where n is the value of num
+def newman_conway(num)
+  raise ArgumentError if num == 0
 
+  output = []
+  i = 1
 
-# Time complexity: ?
-# Space Complexity: ?
-def newman_conway(num)
-  raise NotImplementedError, "newman_conway isn't implemented"
-end
+  while i <= num
+    output << conway_helper(i, output)
+    i += 1
+  end
+  return output.join(" ")
+end
+
+def conway_helper(num, output)
+  return 1 if num < 3
+  return output[num - 1] if output[num - 1]
+  helper = conway_helper(num - 1, output)
+  conway_helper(helper, output) + conway_helper(num - helper, output)
+end

test/max_sub_array_test.rb

@@ -1,9 +1,9 @@
 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]
+    input = [-2, 1, -3, 4, -1, 2, 1, -5, 4]
 
     # Act
     answer = max_sub_array(input)
@@ -25,7 +25,7 @@
 
   it "will work with a totally negative array with the largest element at the rear" do
     # Arrange
-    input = [ -4, -5, -6, -7, -3]
+    input = [-4, -5, -6, -7, -3]
 
     # Act
     answer = max_sub_array(input)
@@ -46,14 +46,14 @@
   end
 
   it "will return nil for an empty array" do
-   # Arrange
-   input = []
+    # Arrange
+    input = []
 
-   # Act
-   answer = max_sub_array(input)
+    # Act
+    answer = max_sub_array(input)
 
-   # Assert
-   expect(answer).must_be_nil
+    # Assert
+    expect(answer).must_be_nil
   end
 
   it "will work for [50, -50, 50]" do
@@ -66,5 +66,4 @@
     # Assert
     expect(answer).must_equal 50
   end
-
-end
+end

test/newman_conway_test.rb

@@ -24,31 +24,30 @@
   end
 
   it "works with base cases" do
-        # Arrange
-        input = 0
-
-        # Act-Assert
-        expect {
-          newman_conway(input)
-        }.must_raise ArgumentError
-
-
-        # Arrange
-        input = 1
-
-        # Act
-        answer = newman_conway(input)
-
-        # Assert
-        expect(answer).must_equal "1"
-
-        # Arrange
-        input = 2
-
-        # Act
-        answer = newman_conway(input)
-
-        # Assert
-        expect(answer).must_equal "1 1"        
+    # Arrange
+    input = 0
+
+    # Act-Assert
+    expect {
+      newman_conway(input)
+    }.must_raise ArgumentError
+
+    # Arrange
+    input = 1
+
+    # Act
+    answer = newman_conway(input)
+
+    # Assert
+    expect(answer).must_equal "1"
+
+    # Arrange
+    input = 2
+
+    # Act
+    answer = newman_conway(input)
+
+    # Assert
+    expect(answer).must_equal "1 1"
   end
 end