LSStaff

Problem Domain

A problem domain is the area of expertise or application that needs to be examined to solve a problem (source: problem domain wiki). It limits the scope of the problem.

LSStaff

Mental Model

A mental model is an explanation of someone's thought process about how something works in the real world (source: wikipedia)

LSStaff

Validation

Example 1

Inputs:

• Target number: 20
• Factors: [3, 5]

Output

• 78

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Example 2

LSStaff

Where to Start?

In this step, if you have a mental model, you can start there. Otherwise, start with the "Data Structure" step and think of how you'd build and manipulate it to get the output. For instance, if it's an array, you'd probably focus on constructing or iterating over a collection.

LSStaff

First Mental Model

Determine a list of all multiples of a set of factors up to a target value, then filter the list of multiples to the unique values. Finally, compute and return the sum of the unique multiples.

1. Create an empty array called multiples that will contain the multiples.
2. Check whether the list of factors is empty. If there are no factors, set the list to [3, 5]
3. For every factor in the factors list:
   1. Set the current_multiple to factor to keep track of the multiples of factor.
   2. While current_multiple < target
      1. Append the current_multiple to multiples.
      2. Add factor to current_multiple.
4. Filter duplicate numbers from multiples.

LSStaff

Example 1

Inputs:

• Target number: 20
• Number to get multiples: [3, 5]

Output

• 78

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Algorithm

LSStaff

def sum_of_multiples(target, factors)
  multiples = []
  factors = [3, 5] if factors.length == 0

  factors.each do |factor|
    current_multiple = factor

    while current_multiple < target
      multiples << current_multiple
      current_multiple += factor

LSStaff

function sumOfMultiples(targetNumber, factors) {
  var multiples = [];
  if (factors.length === 0) {
    factors = [3, 5];
  }

  factors.forEach(function(factor) {
    var currentMultiple;
    for (currentMultiple = factor; currentMultiple < targetNumber; currentMultiple += factor) {
      if (multiples.indexOf(currentMultiple) === -1) {

LSStaff

Validation

Example 6

Inputs:

• Target number: 20
• Factors: [19]

Output

• 19