Add Depth First Search in Ruby

archive/r/ruby/depth-first-search.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+USAGE = 'Usage: please provide a tree in an adjacency matrix form ("0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0") together with a list of vertex values ("1, 3, 5, 2, 4") and the integer to find ("4")'
+
+def usage!
+  warn USAGE
+  exit 1
+end
+
+def parse_list(str)
+  str.split(",").map { Integer(it.strip) }
+rescue ArgumentError, NoMethodError
+  usage!
+end
+
+def matrix(flat)
+  n = Integer(Math.sqrt(flat.size))
+  usage! unless n * n == flat.size
+  flat.each_slice(n).to_a
+end
+
+def dfs(mat, vals, i, target, seen)
+  return true if vals[i] == target
+  return false if seen[i]
+
+  seen[i] = true
+
+  mat[i].each_with_index do |edge, j|
+    next unless edge == 1
+    return true if dfs(mat, vals, j, target, seen)
+  end
+
+  false
+end
+
+tree_s, vals_s, target_s = ARGV
+usage! if tree_s.nil? || vals_s.nil? || target_s.nil?
+
+tree = parse_list(tree_s)
+vals = parse_list(vals_s)
+target = begin
+  Integer(target_s)
+rescue
+  usage!
+end
+
+usage! unless vals.size * vals.size == tree.size
+
+mat = matrix(tree)
+
+puts dfs(mat, vals, 0, target, {})