Add Dijkstra in Ruby

archive/r/ruby/dijkstra.rb

@@ -0,0 +1,89 @@
+# frozen_string_literal: true
+
+USAGE = "Usage: please provide three inputs: a serialized matrix, a source node and a destination node"
+
+def usage!
+  warn USAGE
+  exit 1
+end
+
+def parse_matrix(str)
+  str.split(",").map { Integer(it.strip) }
+rescue ArgumentError, NoMethodError
+  usage!
+end
+
+def build_matrix(flat)
+  n = Integer(Math.sqrt(flat.size))
+  usage! unless n * n == flat.size
+
+  matrix = flat.each_slice(n).to_a
+
+  usage! if matrix.any? { |row| row.any?(&:negative?) }
+
+  matrix
+end
+
+def parse_index(str, n)
+  usage! if str.nil? || str.strip.empty?
+
+  i = Integer(str)
+  usage! unless i.between?(0, n - 1)
+
+  i
+rescue ArgumentError
+  usage!
+end
+
+def dijkstra(matrix, src, dst)
+  n = matrix.size
+  dist = Array.new(n, Float::INFINITY)
+  visited = Array.new(n, false)
+
+  dist[src] = 0
+
+  n.times do
+    u = nil
+    best = Float::INFINITY
+
+    n.times do |i|
+      next if visited[i]
+      next if dist[i] >= best
+
+      best = dist[i]
+      u = i
+    end
+
+    break unless u
+
+    visited[u] = true
+
+    row = matrix[u]
+    base = dist[u]
+
+    row.each_with_index do |w, v|
+      next if w <= 0 || visited[v]
+
+      alt = base + w
+      dist[v] = alt if alt < dist[v]
+    end
+  end
+
+  dist[dst]
+end
+
+matrix_str, src_str, dst_str = ARGV
+usage! if matrix_str.nil? || src_str.nil? || dst_str.nil?
+usage! if matrix_str.strip.empty? || src_str.strip.empty? || dst_str.strip.empty?
+
+matrix = build_matrix(parse_matrix(matrix_str))
+n = matrix.size
+
+src = parse_index(src_str, n)
+dst = parse_index(dst_str, n)
+
+dist = dijkstra(matrix, src, dst)
+
+usage! unless dist.finite?
+
+puts dist.to_i