prefix calculator using stack in javascript

Question

i'm trying to make calculator with RPN (reverse polish notation) input method using stack in javascript.

input : [1, 5, '+', 6, 3, '-', '/', 7, '*']

1 is an operand, push to Stack.

5 is an operand, push to Stack.

'+' is an operator, pop 1 and 5, calculate them and push result to Stack.

6 is an operand, push to Stack.

3 is an operand, push to Stack.

'-' is an operator, pop 6 and 3, subtract them and push result to Stack.

'/' is an operator, pop 6 and 3, divided them and push result to Stack.

7 is an operand, push to Stack.

'*' is an operator, pop 2 and 7, multiply them and push result to Stack.

output : [14]

is there any other alternative to make my code more effective?

const x1 = x.push(1);
const x2 = x.push(5);
const x3 = x.push('+');

x.pop(1);
x.pop(5);
x.pop('+');
x.push(1+5);

const x4 = x.push(6);
const x5 = x.push(3);
const x6 = x.push('-');

x.pop(6);
x.pop(3);
x.pop('-');
x.push(6-3);

const x7 = x.push('/');
x.pop(6);
x.pop(3);
x.pop('/');
x.push(6/3);

const x8 = x.push(7);
const x9 = x.push('*');

x.pop(2);
x.pop(7);
x.pop('*');
x.push(2*7);

console.log(x);

A. This is postfix, not prefix. B. You should just be calling x.pop() with no parameter, and using the results from the pops. Also, you need to create add,subtract, multiply and divide functions that take two parameters each, rather than using +-*/ in your code — ControlAltDel
– ControlAltDel, Commented Sep 4, 2020 at 17:27

Nina Scholz · Accepted Answer · 2020-09-11 06:11:14Z

5

You could take an object for all operators and check if the value of input is an operator, then perform the operation with the reversed popped values of the stack or push the value to the stack.

const
    operators = {
        '+': (a, b) => a + b,
        '-': (a, b) => a - b,
        '*': (a, b) => a * b,
        '/': (a, b) => a / b
    },
    input = [1, 5, '+', 6, 3, '-', '/', 7, '*'],
    stack = [];

input.forEach(value => {
    stack.push(value in operators
        ? operators[value](...stack.splice(-2))
        : value
    );
    console.log(...stack);
});

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Sep 11, 2020 at 6:11

answered Sep 4, 2020 at 18:12

Nina Scholz

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3 Comments

ControlAltDel Over a year ago

Wow this is a remarkably concise implementation! +1

makarov19 Over a year ago

so, we just pull out element from input and push it to new array stack. there's no need to use .pop() ?

Nina Scholz Over a year ago

yes, but stack.splice(-2, 2) delets the last two values of the stack and returns them in an array. this array is spreaded as parameters for the operation.

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