working remove duplicates and longest prefix

lib/practice_exercises.rb

@@ -1,13 +1,44 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n^2)
+# Space Complexity: O(1)
+
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  i = 0
+
+  while i < list.length
+    if list[i] == list[i+1]
+      (i+1..list.length - 1).each do |k|
+        list[k] = list [k+1]
+      end
+      list.pop  # for future reference: pop is O(1)
+    else
+      i += 1
+    end
+  end
+
+  return list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n) because word lengths are pretty finite, else O(m*n)
+# Space Complexity: O(n)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  arr_length = strings.length
+  word_length = strings[0].length
+
+  result = ""
+
+  word_length.times do |i|
+
+    current_letter = strings[0][i]
+
+    arr_length.times do |j|
+      if strings[j][i] != current_letter
+        return result
+      end
+    end
+
+    result << current_letter  # for future reference: push is O(1)
+  end
+
+  return result
 end
-

test/practice_exercises_test.rb

@@ -9,35 +9,45 @@
     it "works for empty arrays" do
       expect(remove_duplicates([])).must_equal []
     end
-
+    
     it "will remove duplicates for longer arrays" do
       expect(remove_duplicates([1, 2, 2, 3, 3, 4])).must_equal [1, 2, 3, 4]
     end
+
+    it "will remove duplicates for even longer arrays" do
+      expect(remove_duplicates([1, 2, 2, 2, 3, 3, 4, 4, 4, 4])).must_equal [1, 2, 3, 4]
+    end
   end
-
+  
   describe "Longest valid substring" do
     it "will work for the README strings" do
       strings = ["flower","flow","flight"]
-
+      
       output = longest_prefix(strings)
-
+      
       expect(output).must_equal "fl"
     end
-
+    
     it "will work for the strings with the common prefix in the rear" do
       strings = ["flower","flow","flight", "fpastafl"]
-
+      
       output = longest_prefix(strings)
-
+      
       expect(output).must_equal "f"
     end
-
+    
     it "will work for the README strings" do
       strings = ["dog","racecar","car"]
-
+      
       output = longest_prefix(strings)
-
+      
       expect(output).must_equal ""
     end
+
+    it "will work for the flower strings" do
+      strings = ["flower", "flower", "flower"]
+      output = longest_prefix(strings)
+      expect(output).must_equal "flower"
+    end
   end
 end