Merge pull request #67 from vbrazo/add-double-linear-search

Search algorithm: Double linear search

DIRECTORY.md

@@ -47,6 +47,7 @@
   * [Binary Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/binary_search.rb)
   * [Depth First Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/depth_first_search.rb)
   * [Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/linear_search.rb)
+  * [Double Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/double_linear_search.rb)
   * [Recursive Linear Search](https://github.com/TheAlgorithms/Ruby/blob/master/searches/recursive_linear_search.rb)
 
 ## Sorting

searches/double_linear_search.rb

@@ -0,0 +1,29 @@
+# Iterate through the array from both sides to find the index of search_item.
+
+def double_linear_search(array, search_item)
+  start_ind = 0
+  end_ind = array.length - 1
+
+  while start_ind <= end_ind
+    return start_ind if array[start_ind] == search_item
+    return end_ind if array[end_ind] == search_item
+
+    start_ind += 1
+    end_ind -= 1
+  end
+
+  # returns -1 if search_item is not found in array
+  -1
+end
+
+puts(double_linear_search([1, 5, 5, 10], 1))
+# => 0
+
+puts(double_linear_search([1, 5, 5, 10], 5))
+# => 1
+
+puts(double_linear_search([1, 5, 5, 10], 100))
+# => -1
+
+puts(double_linear_search([1, 5, 5, 10], 10))
+# => 3