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infix to postfix
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| require "awesome_print" | |
| exp = "1 + 2 * 3" | |
| exp = "9 + 24 / (7 - 3)" | |
| exp = "3 * atan(2/3)" | |
| exp = "(12.3mm - 1')*52 - 473 mm/(4 + 2^3)" | |
| def prec(op) | |
| case op | |
| when "+", "-" | |
| return 10 | |
| when "*", "/" | |
| return 20 | |
| when "^" | |
| return 30 | |
| when "(", ")" | |
| return 40 | |
| else | |
| return nil | |
| end | |
| end | |
| def is_operator(t) | |
| operators = ["-", "+", "*", "/", "^"] | |
| operators.include?(t) | |
| end | |
| # Anything that is not an operator, parenthesis, or space is a operand | |
| def tokenize(exp) | |
| operand = "" | |
| tokens = [] | |
| exp.each_char do |c| | |
| if is_operator(c) || c == "(" || c == ")" | |
| if operand != "" | |
| tokens << operand | |
| operand = "" | |
| end | |
| tokens << c | |
| else | |
| operand << c unless c == " " | |
| end | |
| end | |
| tokens << operand unless operand.empty? | |
| return tokens | |
| end | |
| def infix2postfix(tokens) | |
| output = [] | |
| stack = [] | |
| tokens.each do |token| | |
| if is_operator(token) | |
| while (!stack.empty? && is_operator(stack[-1]) && prec(stack[-1]) >= prec(token)) | |
| output << stack.pop | |
| end | |
| stack << token | |
| next | |
| end | |
| if token == "(" | |
| stack.push token | |
| next | |
| end | |
| if token == ")" | |
| while stack[-1] && stack[-1] != "(" | |
| output << stack.pop | |
| end | |
| stack.pop | |
| next | |
| end | |
| output << token | |
| end # do loop | |
| while (!stack.empty?) | |
| output << stack.pop | |
| end | |
| return output | |
| end | |
| def eval_postfix(arr) | |
| stack = [] | |
| arr.each do |elm| | |
| end | |
| end | |
| puts exp | |
| tokens = tokenize exp | |
| puts "Tokens:" | |
| ap tokens | |
| postfix = infix2postfix(tokens) | |
| puts | |
| puts "Postfix:" | |
| ap postfix |
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