Logic and algorithms without the mystery

Break the problem down

Define normal examples, boundaries, and errors. If you cannot predict the output for a small input, the rule is not clear yet.

• What do I receive?
• Which constraints exist?
• What must I return?
• What happens with zero, empty, or repeated values?

Pseudocode first

Pseudocode keeps syntax out of the conversation while you are still designing the solution.

FOR each order
  IF order is paid
    add order.total
RETURN sum

Cost is part of the solution

Traversing a collection once is usually O(n). Two nested traversals often approach O(n²). Big O describes growth, not today's milliseconds.

const paidTotal = orders
  .filter((order) => order.paid)
  .reduce((total, order) => total + order.total, 0);