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October 5, 2020 01:57
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Ruby script to convert a formula string to a RPN.
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#! /usr/local/bin/ruby | |
#********************************************************* | |
# Ruby script to convert string to RPN. | |
# (Unary operators are not supported) | |
#********************************************************* | |
class String | |
RE_0 = Regexp.new('\s+|\=') | |
RE_1 = Regexp.new('[\d\.]+|[()*/+\-]') | |
RE_D = Regexp.new('\d+') | |
RE_K_0 = Regexp.new('\(') | |
RE_K_1 = Regexp.new('\)') | |
RE_K_2 = Regexp.new('[()]') | |
PRI = {"*" => 3, "/" => 3, "+" => 2, "-" => 2, "(" => 1, ")" => 1} | |
def to_rpn | |
stack = [] | |
rpn = [] | |
self.gsub(RE_0, "").scan(RE_1).each do |t| | |
case t | |
when RE_D | |
rpn << t | |
when RE_K_0 | |
stack << t | |
when RE_K_1 | |
while stack[-1] != "(" | |
s = stack.pop | |
rpn << s if s !~ RE_K_2 | |
end | |
stack.pop | |
else | |
while stack != [] && PRI[stack[-1]] >= PRI[t] | |
rpn << stack.pop | |
end | |
stack << t | |
end | |
end | |
until stack == [] | |
s = stack.pop | |
rpn << s if s !~ RE_K_2 | |
end | |
return rpn.join(" ") | |
end | |
end | |
if __FILE__ == $0 | |
f = $stdin.gets.chomp | |
exit if f == "" | |
puts f.to_rpn | |
end |
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