Update and rename RPNSolver.md to solveRPN.md

This commit is contained in:
Angelos Chalaris
2018-01-01 19:03:47 +02:00
committed by GitHub
parent 764cbcd1c2
commit 30c88a8a38
2 changed files with 34 additions and 28 deletions

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### RPNSolver
Solves the given reverse polish notation
``` js
const RPNSolver = RPN => {
const OPERATORS = {'*' : (a,b) => a * b, '+' : (a,b) => a + b, '-' : (a,b) => a - b, '/' : (a,b) => a / b, '**': (a,b) => a ** b}
const [stack,solve] = [[],RPN.replace(/\^/g,'**').split(/\s+/g).filter(el => !/\s+/.test(el) && el !== '')]
solve.forEach(symbol => {
if(!isNaN(parseFloat(symbol)) && isFinite(symbol)) {stack.push(symbol)}
else if (Object.keys(OPERATORS).includes(symbol)) {
const [a,b] = [stack.pop(),stack.pop()]
stack.push(OPERATORS[symbol](parseFloat(b),parseFloat(a)))
} else { throw `${symbol} is not a recognized symbol` }
}
)
if(stack.length === 1) return stack.pop()
else throw `${RPN} is not a proper RPN. Please check it and try again`
}
```
```js
RPNSolver('15 7 1 1 + - / 3 * 2 1 1 + + -'); // 5
RPNSolver('3 5 6 + *'); //33
RPNSolver('2 4 / 5 6 - *'); //-0.5
RPNSolver('2 3 ^'); //8
RPNSolver('2 3 ^'); //8
```

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