Add Maximum Subarray in Ruby

archive/r/ruby/maximum-subarray.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+USAGE = 'Usage: Please provide a list of integers in the format: "1, 2, 3, 4, 5"'
+
+def usage!
+  warn USAGE
+  exit 1
+end
+
+def parse_list(str)
+  str.split(",").map { Integer(it.strip) }
+rescue ArgumentError, NoMethodError
+  usage!
+end
+
+def max_subarray_sum(arr)
+  return arr.first if arr.length == 1
+  return arr.sum if arr.none?(&:negative?)
+
+  current = max = arr.first
+
+  arr[1..].each do |x|
+    current = [x, current + x].max
+    max = [max, current].max
+  end
+
+  max
+end
+
+raw = ARGV.first
+usage! if raw.nil? || raw.strip.empty?
+
+arr = parse_list(raw)
+usage! if arr.length < 1
+
+puts max_subarray_sum(arr)