Merge pull request #96 from jsca-kwok/jk-sorted-squares

Add algorithm for returning sorted squares

.gitignore

@@ -0,0 +1 @@
+*.DS_Store

DIRECTORY.md

@@ -7,6 +7,7 @@
     * [Find All Duplicates In An Array](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_all_duplicates_in_an_array.rb)
     * [Find The Highest Altitude](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_the_highest_altitude.rb)
     * [Get Products Of All Other Elements](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
+    * [Sort Squares of an Array](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/sort_squares_of_an_array.rb)
   * Binary Trees
     * [Inorder Traversal](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/inorder_traversal.rb)
     * [Invert](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/binary_trees/invert.rb)

data_structures/arrays/sort_squares_of_an_array.rb

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+# Arrays - Sorted Squares
+
+# Algorithm challenge description:
+# Given an integer array nums sorted in non-decreasing order
+# return an array of the squares of each number sorted in non-decreasing order.
+# Input: [4, -1, -9, 2]
+# Output: [1, 4, 16, 81]
+
+#
+# Approach 1: is using Ruby function (for sure)!
+#
+
+def sorted_squares(nums)
+  nums.map! { |num| num**2 }.sort
+end
+print(sorted_squares([4, -1, -9, 2]))
+
+#
+# Approach 2: is using bubble sort
+#
+
+def bubble_sort(array)
+  array_length = array.size
+  return array if array_length <= 1
+  loop do
+    swapped = false
+    (array_length - 1).times do |i|
+      if array[i] > array[i + 1]
+        array[i], array[i + 1] = array[i + 1], array[i]
+        swapped = true
+      end
+    end
+    break unless swapped
+  end
+  array
+end
+
+#
+# Time complexity: O(n logn), where n is the length of the array.
+# Space complexity: O(n) or O(logn)
+#
+
+def sorted_squares(nums)
+  # This takes O(n)
+  nums.map! { |num| num**2 }
+  # This can take Ο(n logn)
+  bubble_sort(nums)
+end
+print(sorted_squares([4, -1, -9, 2]))
+
+#
+# Approach 3: solving without ruby sort method. Using two-pointers
+#
+# Time complexity: O(n), where n is the length of the array.
+# Space complexity: O(n), if you take output into account and O(1) otherwise.
+#
+def sorted_squares(nums)
+  p1 = 0
+  p2 = nums.length - 1
+  # since we're returing the result in ascending order,
+  # we'll fill in the array from the end
+  max_index = p2
+  output = []
+  while p1 < p2
+    nums1_square = nums[p1] * nums[p1]
+    nums2_square = nums[p2] * nums[p2]
+    if nums1_square < nums2_square
+      output[max_index] = nums2_square
+      p2 -= 1
+    elsif nums1_square > nums2_square
+      output[max_index] = nums1_square
+      p1 += 1
+    else
+      output[max_index] = nums1_square
+      max_index -= 1
+      output[max_index] = nums2_square
+      p1 += 1
+      p2 -= 1
+    end
+    max_index -= 1
+  end
+  # to account for any remaining value left in the input array
+  output[max_index] = nums[p1] * nums[p2] if p1 == p2
+  output
+end
+
+print(sorted_squares([4, -1, -9, 2]))