Merge pull request #99 from jsca-kwok/jk-remove-element

Remove a given value from an array

DIRECTORY.md

@@ -9,7 +9,8 @@
     * [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)
     * [Two Sum](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/two_sum.rb)
-    * [Two Sum Ii](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/two_sum_ii.rb)
+    * [Two Sum II](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/two_sum_ii.rb)
+    * [Remove Elements](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/remove_elements.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/remove_elements.rb

@@ -0,0 +1,54 @@
+# Arrays - Remove Elements
+#
+# Given an array nums and a value val, remove all instances of that value in-place and return the new length.
+# Do not allocate extra space for another array, 
+# you must do this by modifying the input array in-place with O(1) extra memory.
+# The order of elements can be changed. It doesn't matter what you leave beyond the new length.
+#
+# Example
+#
+# Input: nums = [3,2,2,3], val = 3
+# Output: 2, nums = [2,2]
+#
+# Input: nums = [0,1,2,2,3,0,4,2], val = 2
+# Output: 5, nums = [0,1,4,0,3]
+
+#
+# Approach 1: Use `delete_if` Ruby method
+#
+# Time complexity: O(n)
+#
+def remove_elements(nums, val)
+  nums.delete_if{ |num| num == val }
+  nums.length
+end
+
+puts remove_elements([3,2,2,3], 3)
+# => 2
+puts remove_elements([0,1,2,2,3,0,4,2], 2)
+# => 5
+
+#
+# Approach 2: Use `delete_at`, `unshift`, and `shift` Ruby method
+#
+# Time complexity: O(n)
+#
+def remove_elements(nums, val)
+  result_length = nums.length
+  shift_length = 0
+  nums.each_with_index do |num, i|
+    if num == val 
+      nums.delete_at(i)
+      nums.unshift('removed')
+      result_length -=1
+      shift_length += 1
+    end
+  end
+  nums.shift(shift_length)
+  result_length
+end
+
+puts remove_elements([3,2,2,3], 3)
+# => 2
+puts remove_elements([0,1,2,2,3,0,4,2], 2)
+# => 5