Good morning! Here's our prompt for today.

Let's build a very basic calculator by programming it! You've probably seen one that look similar to this:

But we won't be building a physical calculator (HardwareDaily will need to wait!)-- instead, we'll be writing a simple program that can serve as one. Can you write a function that will evaluate a simple expression string without using your language's eval method?

1const expr = "2 + 2";
2calculator(expr)
3// 4

It should also be able to handle positive and negative symbols +,-, parentheses (), and spaces.

1let expr = "3 - 1 + 2";
2calculator(expr)
3// 4
4
5expr = "(2+(4+2)-1)-(5+8)"
6calculator(expr)
7// -6

Assume for now that you don't need to handle multiplication or division cases.

Constraints

• Length of the given string <= 100000
• The numbers present in the string will be a single digit number
• Expected time complexity : O(n)
• Expected space complexity : O(n)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');

​

function calculator(str) {

  // implement this method

  return str;

}

​

try {

  assert.equal(calculator('2 + 2'), 4);

​

  console.log('PASSED: ' + "assert.equal(calculator('2 + 2'), 4)");

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(calculator('(2+2) - 3'), 1);

​

  console.log('PASSED: ' + "assert.equal(calculator('(2+2) - 3'), 1)");

} catch (err) {

  console.log(err);

}

​

Here's our guided, illustrated walk-through.

How do I use this guide?