Space - Jessica

lib/exercises.rb

@@ -1,21 +1,76 @@
 
 # This method will return an array of arrays.
 # Each subarray will have strings which are anagrams of each other
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
+
+# hash function that assigns each letter a value
+def alphabet_keys()
+  alphabet = "abcdefghijklmnopqrstuvwxyz".split('')
+  alphabet_keys = {}
+  alphabet.length.times do |i|
+    alphabet_keys[alphabet[i]] = i + 1
+  end
+
+  return alphabet_keys
+end
 
 def grouped_anagrams(strings)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  return [] if strings == []
+
+  alphabet_keys = alphabet_keys()
+  string_keys = {}
+
+  # iterate through each string
+  strings.each do |str|
+    key = 0
+    # use alphabet_keys to assign each word a key by adding together values of each letter in the word
+    str.split('').each do |l|
+      key += alphabet_keys[l]
+    end
+    # if key exists, add word to that key
+    if string_keys[key]
+      string_keys[key].push(str)
+    else # otherwise create a new key-value pair
+      string_keys[key] = [str]
+    end
+  end
+
+  grouped_anagrams = []
+  string_keys.each do |k, v|
+    grouped_anagrams.push(v)
+  end
+
+  return grouped_anagrams
 end
 
 # This method will return the k most common elements
 # in the case of a tie it will select the first occuring element.
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def top_k_frequent_elements(list, k)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
-end
+  return [] if list.empty?
+  frequency = {}
+  list.each do |i|
+    frequency[i] ? (frequency[i] += 1) : (frequency[i] = 1)
+  end
+
+  nums = []
+  unique = list.uniq
+  max = frequency.values.max
 
+  until max == 0 || nums.length == k
+    unique.each do |i|
+      break if nums.length == k
+      if frequency[i] == max
+        nums << i
+      end
+    end
+    max -= 1
+  end
+
+  return nums
+end
 
 # This method will return the true if the table is still
 #   a valid sudoku table.

test/exercises_test.rb

@@ -81,6 +81,18 @@
       expect(answer.sort).must_equal [1,2]
     end
 
+    it "works with example 1.5" do
+      # Arrange
+      list = [2,1,1,2,2,3]
+      k = 2
+
+      # Act
+      answer = top_k_frequent_elements(list, k)
+
+      # Assert
+      expect(answer).must_equal [2,1]
+    end
+
     it "works with example 2" do
       # Arrange
       list = [1]