Add interpolation search algorithm

searches/interpolation_search.rb

@@ -0,0 +1,39 @@
+# Performs interpolation search on a sorted numeric array.
+# Returns the index of the target element or -1 when target is absent.
+# Raises ArgumentError if the input array is not sorted in ascending order.
+def interpolation_search(array, target)
+  raise ArgumentError, 'Input must be an array' unless array.is_a?(Array)
+  return -1 if array.empty?
+
+  unless array.each_cons(2).all? { |left, right| left <= right }
+    raise ArgumentError, 'Array must be sorted in ascending order'
+  end
+
+  left = 0
+  right = array.length - 1
+
+  while left <= right && target >= array[left] && target <= array[right]
+    return left if array[left] == target
+    return right if array[right] == target
+
+    value_range = array[right] - array[left]
+    if value_range.zero?
+      return array[left] == target ? left : -1
+    end
+
+    position = left + ((target - array[left]) * (right - left) / value_range)
+    return -1 if position < left || position > right
+
+    current = array[position]
+
+    if current == target
+      return position
+    elsif current < target
+      left = position + 1
+    else
+      right = position - 1
+    end
+  end
+
+  -1
+end

searches/interpolation_search_test.rb

@@ -0,0 +1,31 @@
+require 'minitest/autorun'
+require_relative './interpolation_search'
+
+class TestInterpolationSearch < Minitest::Test
+  def test_finds_existing_element
+    array = [2, 4, 6, 8, 10, 12, 14]
+    assert_equal 3, interpolation_search(array, 8)
+  end
+
+  def test_returns_negative_one_for_missing_element
+    array = [10, 20, 30, 40, 50]
+    assert_equal(-1, interpolation_search(array, 35))
+  end
+
+  def test_handles_empty_array
+    assert_equal(-1, interpolation_search([], 7))
+  end
+
+  def test_handles_uniform_values
+    array = [5, 5, 5, 5]
+    assert_equal 0, interpolation_search(array, 5)
+    assert_equal(-1, interpolation_search(array, 4))
+  end
+
+  def test_raises_when_array_not_sorted
+    array = [3, 1, 2]
+    assert_raises ArgumentError do
+      interpolation_search(array, 1)
+    end
+  end
+end