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27 lines
591 B
Ruby
27 lines
591 B
Ruby
# Dijkstra's Two-Stack Algorithm for Expression Evaluation,
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# see examples in test/expressions_test.rb
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module Expressions
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def self.evaluate(expression)
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operators = []
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values = []
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expression.each_char do |ch|
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next if ch == '('
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if ch == ')'
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operator = operators.shift
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value2 = values.shift
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value1 = values.shift
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result = value1.send(operator, value2)
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values.unshift(result)
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elsif '+-*/'.include?(ch)
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operators.unshift(ch)
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else
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values.unshift(ch.to_i)
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end
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end
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values.shift
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end
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end
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