b2849682d3
I'm writing a function that returns the total number of ways a cashier can make change given the `amount` of change that the customer needs and an array of `coins` from which to create the change. My solution conceptually works but it actually does not return the results I am expecting because I cannot create a Set of Map<A, B> in JavaScript. I'm also somewhat sure that InterviewCake is expecting a less computationally expensive answer.
102 lines
2.4 KiB
TypeScript
102 lines
2.4 KiB
TypeScript
// The denomination of a coin.
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type Coin = number;
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// The amount of change remaining.
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type Amount = number;
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// Mapping of Coin -> Int
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type CoinBag = Map<Coin, number>;
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function createCoinBag(coins: Coin[]): CoinBag {
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const result = new Map();
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for (const coin of coins) {
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result.set(coin, 0);
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}
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return result;
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}
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// This algorithm should work conceptual, but it does not actually
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// work. JavaScript uses reference equality when constructing a Set<Map<A,B>>,
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// so my result.size returns a higher number than I expect because it contains
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// many duplicate entries.
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//
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// Conceptually, I'm not sure this solution is optimal either -- even after I
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// can dedupe the entries in `result`.
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function changePossibilities(amt: Amount, coins: Coin[]): number {
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if (amt === 0) {
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return 1;
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}
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const result: Set<CoinBag> = new Set();
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const q: [Coin, Amount, CoinBag][] = [];
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for (const coin of coins) {
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const bag = createCoinBag(coins);
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bag.set(coin, 1);
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q.push([coin, amt - coin, bag]);
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}
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while (q.length > 0) {
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const [coin, amt, bag] = q.shift();
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console.log([coin, amt, bag]);
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if (amt === 0) {
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result.add(bag);
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} else if (amt < 0) {
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continue;
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} else {
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for (const c of coins) {
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const bagCopy = new Map(bag);
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const value = bagCopy.get(c);
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bagCopy.set(c, value + 1);
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q.push([c, amt - c, bagCopy]);
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}
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}
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}
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console.log(result);
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return result.size;
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}
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// Tests
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let desc = "sample input";
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let actual = changePossibilities(4, [1, 2, 3]);
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let expected = 4;
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assertEqual(actual, expected, desc);
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desc = "one way to make zero cents";
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actual = changePossibilities(0, [1, 2]);
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expected = 1;
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assertEqual(actual, expected, desc);
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desc = "no ways if no coins";
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actual = changePossibilities(1, []);
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expected = 0;
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assertEqual(actual, expected, desc);
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desc = "big coin value";
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actual = changePossibilities(5, [25, 50]);
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expected = 0;
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assertEqual(actual, expected, desc);
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desc = "big target amount";
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actual = changePossibilities(50, [5, 10]);
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expected = 6;
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assertEqual(actual, expected, desc);
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// I think InterviewCake designed this assertion to be computationally
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// expensive.
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desc = "change for one dollar";
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actual = changePossibilities(100, [1, 5, 10, 25, 50]);
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expected = 292;
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assertEqual(actual, expected, desc);
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function assertEqual(a, b, desc) {
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if (a === b) {
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console.log(`${desc} ... PASS`);
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} else {
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console.log(`${desc} ... FAIL: ${a} != ${b}`);
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}
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}
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