49 lines
1.8 KiB
Markdown
49 lines
1.8 KiB
Markdown
### solveRPN
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Solves the given mathematical expression in [reverse polish notation](https://en.wikipedia.org/wiki/Reverse_Polish_notation).
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Throws appropriate errors if there are unrecognized symbols or the expression is wrong.
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Use a dictionary, `OPERATORS` to specify each operator's matching mathematical operation.
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Use `String.replace()` with a regular expression to replace `^` with `**`, `String.split()` to tokenize the string and `Array.filter()` to remove empty tokens.
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Use `Array.forEach()` to parse each `symbol`, evaluate it as a numeric value or operator and solve the mathematical expression.
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Numeric values are converted to floating point numbers and pushed to a `stack`, while operators are evaluated using the `OPERATORS` dictionary and pop elements from the `stack` to apply operations.
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```js
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const solveRPN = rpn => {
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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) => a / b,
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'**': (a, b) => a ** b
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};
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const [stack, solve] = [
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[],
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rpn
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.replace(/\^/g, '**')
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.split(/\s+/g)
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.filter(el => !/\s+/.test(el) && el !== '')
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];
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solve.forEach(symbol => {
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if (!isNaN(parseFloat(symbol)) && isFinite(symbol)) {
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stack.push(symbol);
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} else if (Object.keys(OPERATORS).includes(symbol)) {
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const [a, b] = [stack.pop(), stack.pop()];
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stack.push(OPERATORS[symbol](parseFloat(b), parseFloat(a)));
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} else {
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throw `${symbol} is not a recognized symbol`;
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}
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});
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if (stack.length === 1) return stack.pop();
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else throw `${rpn} is not a proper RPN. Please check it and try again`;
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};
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```
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```js
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solveRPN('15 7 1 1 + - / 3 * 2 1 1 + + -'); // 5
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solveRPN('3 5 6 + *'); //33
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solveRPN('2 4 / 5 6 - *'); //-0.5
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solveRPN('2 3 ^'); //8
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solveRPN('2 3 ^'); //8
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```
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