Leaves - Yitgop

Gemfile.lock

@@ -0,0 +1,30 @@
+GEM
+  remote: http://rubygems.org/
+  specs:
+    ansi (1.5.0)
+    builder (3.2.3)
+    minitest (5.10.3)
+    minitest-reporters (1.3.8)
+      ansi
+      builder
+      minitest (>= 5.0)
+      ruby-progressbar
+    minitest-skip (0.0.1)
+      minitest (~> 5.0)
+    rake (12.3.0)
+    ruby-progressbar (1.10.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  minitest
+  minitest-reporters
+  minitest-skip
+  rake
+
+RUBY VERSION
+   ruby 2.5.1p57
+
+BUNDLED WITH
+   1.17.3

lib/reverse_sentence.rb

@@ -1,6 +1,73 @@
 # A method to reverse the words in a sentence, in place.
-# Time complexity: ?
-# Space complexity: ?
-def reverse_sentence(my_sentence)
-  raise NotImplementedError
+# Time complexity: O(n2)
+# Space complexity: O(n)
+def reverse_sentence(my_sentence) 
+  #Step_0: Screen out all sentences that doesn't need to be/can't be reversed
+  if my_sentence == nil || my_sentence == "" || my_sentence.include?("\s") == false
+    return my_sentence
+    exit
+  end
+
+  #Step_1: Reverse all characters within the string in place
+  sentence_pairs = pairs_helper(my_sentence.length)
+  i = 1
+  (sentence_pairs).times do
+    temp = my_sentence[i-1]
+    my_sentence[i-1] = my_sentence[-i]
+    my_sentence[-i] = temp
+    i += 1
+  end
+
+  #Step_2: Find all whitespace index(es) within the current string
+  space_indexes = (0...my_sentence.length).find_all { |c| my_sentence[c] == " " }
+
+  #Step_3: Reverse all characters for each word based on the whitespace index(es)
+  #Step_3.1: Reverse the first word in the string
+  word_pairs = pairs_helper(space_indexes[0])
+  i = 1
+  (word_pairs).times do
+    temp = my_sentence[i-1]
+    my_sentence[i-1] = my_sentence[space_indexes[0]-i]
+    my_sentence[space_indexes[0]-i] = temp
+    i += 1
+  end
+  #Step_3.2: reverse the last word in the string
+  word_pairs = pairs_helper((my_sentence.length - 1) - space_indexes[-1])
+  i = 1
+  (word_pairs).times do
+    temp = my_sentence[-i]
+    my_sentence[-i] = my_sentence[space_indexes[-1]+i]
+    my_sentence[space_indexes[-1]+i] = temp
+    i += 1
+  end
+  #Step_3.3: reverse the words in between (if any)
+  i = 0
+  if space_indexes.length == 1
+    return my_sentence
+  else
+    until i == (space_indexes.length - 1)
+      if my_sentence[space_indexes[i]+1] != " "
+        word_pairs = pairs_helper(space_indexes[i+1]-space_indexes[i]-1)
+        n = 1
+        (word_pairs).times do
+          temp = my_sentence[space_indexes[i]+n]
+          my_sentence[space_indexes[i]+n] = my_sentence[space_indexes[i+1]-n]
+          my_sentence[space_indexes[i+1]-n] = temp
+          n += 1
+        end
+      end
+      i += 1
+    end
+    return my_sentence
+  end
 end
+
+# Helper method to determin pairs of character that needs to be swapped
+def pairs_helper(length)
+  if length % 2 == 0
+    pairs = length / 2
+  else
+    pairs = (length - 1) / 2
+  end
+  return pairs
+end

lib/sort_by_length.rb

@@ -1,7 +1,24 @@
 # A method which will return an array of the words in the string
-#  sorted by the length of the word.
-# Time complexity: ?
-# Space complexity: ?
+# sorted by the length of the word.
+# Time complexity: O(n2)
+# Space complexity: O(n)
+
 def sort_by_length(my_sentence)
-  raise NotImplementedError, "Method not implemented"
-end
+  #Step_1: break the sentence into an array of words
+  my_array = my_sentence.split(/\W+/)
+  #Step_2: compare the words and sort the array
+  i = 0
+  while i < my_array.length-1
+    j = 0
+    while j < my_array.length-i-1
+      if my_array[j].length > my_array[j+1].length
+        temp = my_array[j]
+        my_array[j] = my_array[j+1]
+        my_array[j+1] = temp
+      end
+      j += 1
+    end
+    i += 1
+  end
+  return my_array
+end