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Daily Challenge #312 - Describe the Function

#challenge

You have to create a function calcType, which receives 3 arguments: 2 numbers, and the result of an unknown operation performed on them (also a number).

Based on those 3 values you have to return a string, that describes which operation was used to get the given result.

The possible return strings are: "addition", "subtraction", "multiplication", "division".

In case of division you should expect that the result of the operation is obtained by using / operator on the input values

Example:

calcT_type(1, 2, 3) --> 1 ? 2 = 3 --> "addition"

Tests

calc_type(1, 2, 3)
calc_type(10, 5, 5)
calc_type(10, 4, 40)
calc_type(9, 5, 1.8)

Good luck!

This challenge comes from ridokai on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!

Top comments (8)

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qm3ster profile image
Mihail Malo • • Edited

JavaScript

stupidly golfed:

calc_type=(a,b,c)=>[...'+-*/'].find(x=>eval(a+x+b+'=='+c))
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reasonable:

const ops = '+-*/'.split('').map(x => [x, new Function('a', 'b', 'c', `return (a ${x} b) === c`)])
const calc_type = (a, b, c) => ops.find(([x,f]) => f(a,b,c))?.[0]
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optimized:

function calc_type(a, b, c) {
  switch (c) {
    case a + b: return '+'
    case a - b: return '-'
    case a * b: return '*'
    case a / b: return '/'
  }
}
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Guess what, flow control is expensive! Inlining saves the day, and case is number one.

Both of these are slower, despite not having to calculate the "expensive" division operation:

const ops = [
  (a, b) => a + b,
  (a, b) => a - b,
  (a, b) => a * b,
  (a, b) => a / b,
]
const calc_type = (a, b, c) => strs[ops.findIndex(f => f(a, b) === c)]
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const ops = [
  (a, b, c) => (a + b) === c,
  (a, b, c) => (a - b) === c,
  (a, b, c) => (a * b) === c,
  (a, b, c) => (a / b) === c,
]
const calc_type = (a, b, c) => strs[ops.findIndex(f => f(a, b, c))]
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bugb profile image
bugb •

How about:

2 + 2=4
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and :

2 * 2 = 4
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Or one of these number is 0

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qm3ster profile image
Mihail Malo •

there's only

  • x + 0 == x - 0 (== x)

  • x * 1 == x / 1 (== x)

  • 2 + 2 == 2 * 2

  • 4 - 2 == 4 / 2 (reverse)

Right? What did you mean with

one of these numbers is 0

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bugb profile image
bugb •

You are correct, I mean:

±n / 0 == ±∞
0 * 0 == 0 + 0 == 0 - 0
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Thread Thread
 
qm3ster profile image
Mihail Malo •

If we're talking IEEE754-like floats, there's also NaN :v

  • NaN + a == NaN - b == NaN * c == NaN / d == NaN % e == f + NaN == g - NaN == h * NaN == i / NaN == j % NaN (== NaN)
  • inf + a == inf - b == inf * c == inf / d == f + inf == h * inf (== inf)
  • -inf + a == -inf - b == -inf * c == -inf / d == f + -inf == h * -inf (== -inf)
  • inf - inf == inf / inf (== NaN)
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peter279k profile image
peter279k •

Python:

def calc_type(a, b, res):
    if a + b == res:
        return "addition"
    if a - b == res:
        return "subtraction"
    if a * b == res:
        return "multiplication"
    if a / b == res:
        return "division"
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matrossuch profile image
Mat-R-Such •

Python:

def calc_type(a, b, res):
    if a + b == res:    return "addition"
    elif a - b == res:  return "subtraction"
    elif a / b == res:  return "division"
    elif a * b == res:  return "multiplication"
    else:   return "Error 404"
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qm3ster profile image
Mihail Malo •

Can the first two numbers be negative? fractional? +/- inf? NaN?

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