freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/rosetta-code/count-the-coins.md

title	id	challengeType	forumTopicId
Count the coins	59713bd26bdeb8a594fb9413	5	302238

Description

There are four types of common coins in US currency:

• quarters (25 cents)
• dimes (10 cents)
• nickels (5 cents), and
• pennies (1 cent)

There are six ways to make change for 15 cents:

• A dime and a nickel
• A dime and 5 pennies
• 3 nickels
• 2 nickels and 5 pennies
• A nickel and 10 pennies
• 15 pennies

Instructions

Implement a function to determine how many ways there are to make change for a dollar using these common coins (1 dollar = 100 cents)

Tests

tests:
  - text: <code>countCoins</code> should be a function.
    testString: assert(typeof countCoins === 'function');
  - text: <code>countCoins()</code> should return 242.
    testString: assert.equal(countCoins(), 242);

Challenge Seed

function countCoins() {

  return true;
}

Solution

function countCoins() {
  let t = 100;
  const operands = [1, 5, 10, 25];
  const targetsLength = t + 1;
  const operandsLength = operands.length;
  t = [1];

  for (let a = 0; a < operandsLength; a++) {
    for (let b = 1; b < targetsLength; b++) {
      // initialise undefined target
      t[b] = t[b] ? t[b] : 0;

      // accumulate target + operand ways
      t[b] += (b < operands[a]) ? 0 : t[b - operands[a]];
    }
  }

  return t[targetsLength - 1];
}