Data commit

Task/Arithmetic-evaluation/Ruby/arithmetic-evaluation-1.rb

@@ -0,0 +1,100 @@
+$op_priority = {"+" => 0, "-" => 0, "*" => 1, "/" => 1}
+
+class TreeNode
+  OP_FUNCTION = {
+    "+" => lambda {|x, y| x + y},
+    "-" => lambda {|x, y| x - y},
+    "*" => lambda {|x, y| x * y},
+    "/" => lambda {|x, y| x / y}}
+  attr_accessor :info, :left, :right
+
+  def initialize(info)
+    @info = info
+  end
+
+  def leaf?
+    @left.nil? and @right.nil?
+  end
+
+  def to_s(order)
+    if leaf?
+      @info
+    else
+      left_s, right_s = @left.to_s(order), @right.to_s(order)
+
+      strs = case order
+             when :prefix  then [@info, left_s, right_s]
+             when :infix   then [left_s, @info, right_s]
+             when :postfix then [left_s, right_s, @info]
+             else               []
+             end
+
+      "(" + strs.join(" ") + ")"
+    end
+  end
+
+  def eval
+    if !leaf? and operator?(@info)
+      OP_FUNCTION[@info].call(@left.eval, @right.eval)
+    else
+      @info.to_f
+    end
+  end
+end
+
+def tokenize(exp)
+  exp
+    .gsub('(', ' ( ')
+    .gsub(')', ' ) ')
+    .gsub('+', ' + ')
+    .gsub('-', ' - ')
+    .gsub('*', ' * ')
+    .gsub('/', ' / ')
+    .split(' ')
+end
+
+def operator?(token)
+  $op_priority.has_key?(token)
+end
+
+def pop_connect_push(op_stack, node_stack)
+  temp = op_stack.pop
+  temp.right = node_stack.pop
+  temp.left = node_stack.pop
+  node_stack.push(temp)
+end
+
+def infix_exp_to_tree(exp)
+  tokens = tokenize(exp)
+  op_stack, node_stack = [], []
+
+  tokens.each do |token|
+    if operator?(token)
+      # clear stack of higher priority operators
+      until (op_stack.empty? or
+             op_stack.last.info == "(" or
+             $op_priority[op_stack.last.info] < $op_priority[token])
+        pop_connect_push(op_stack, node_stack)
+      end
+
+      op_stack.push(TreeNode.new(token))
+    elsif token == "("
+      op_stack.push(TreeNode.new(token))
+    elsif token == ")"
+      while op_stack.last.info != "("
+        pop_connect_push(op_stack, node_stack)
+      end
+
+      # throw away the '('
+      op_stack.pop
+    else
+      node_stack.push(TreeNode.new(token))
+    end
+  end
+
+  until op_stack.empty?
+    pop_connect_push(op_stack, node_stack)
+  end
+
+  node_stack.last
+end

Task/Arithmetic-evaluation/Ruby/arithmetic-evaluation-2.rb

@@ -0,0 +1,8 @@
+exp = "1 + 2 - 3 * (4 / 6)"
+puts("Original: " + exp)
+
+tree = infix_exp_to_tree(exp)
+puts("Prefix: " + tree.to_s(:prefix))
+puts("Infix: " + tree.to_s(:infix))
+puts("Postfix: " + tree.to_s(:postfix))
+puts("Result: " + tree.eval.to_s)