Binary search

https://codility.com/media/train/12-BinarySearch.pdf

Author: mrhead

binary_search.rb

@@ -0,0 +1,31 @@
+# https://codility.com/media/train/12-BinarySearch.pdf
+
+def binary_search(a, x)
+  n = a.size
+  back = 0
+  front = n - 1
+  result = -1
+
+  while back <= front
+    middle = (back + front) / 2
+    if a[middle] <= x
+      back = middle + 1
+      result = middle if a[middle] == x
+    else
+      front = middle - 1
+    end
+  end
+  result
+end
+
+require 'minitest/autorun'
+
+class Tests < MiniTest::Unit::TestCase
+  def test_example_input
+    assert_equal 5, binary_search([12, 15, 15, 19, 24, 31, 53, 59, 60], 31)
+  end
+
+  def test_not_found
+    assert_equal -1, binary_search([10, 20, 30], 15)
+  end
+end