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36 lines
733 B
JavaScript
36 lines
733 B
JavaScript
// Wikipedia: https://en.wikipedia.org/wiki/Reverse_Polish_notation
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function calcRPN (expression) {
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const operators = {
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'+': (a, b) => a + b,
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'-': (a, b) => a - b,
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'*': (a, b) => a * b,
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'/': (a, b) => b / a
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}
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const tokens = expression.split(' ')
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const stack = []
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tokens.forEach(token => {
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const operator = operators[token]
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if (typeof operator === 'function') {
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const a = stack.pop()
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const b = stack.pop()
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const result = operator(a, b)
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stack.push(result)
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} else {
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stack.push(parseFloat(token))
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}
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})
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return stack.pop()
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}
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console.log(calcRPN('2 2 2 * +') === 6)
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console.log(calcRPN('2 2 + 2 *') === 8)
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console.log(calcRPN('6 9 7 + 2 / + 3 *') === 42)
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