WIPP

lib/bill-math.js

@@ -0,0 +1,38 @@
+const uuid = require('uuid')
+
+// Custom algorith for two cassettes. For three or more denominations, we'll need
+// to rethink this. Greedy algorithm fails to find *any* solution in some cases.
+// Dynamic programming may be too inefficient for large amounts.
+//
+// We can either require canononical denominations for 3+, or try to expand
+// this algorithm.
+exports.makeChange = function makeChange (cartridges, amount) {
+  // Note: Everything here is converted to primitive numbers,
+  // since they're all integers, well within JS number range,
+  // and this is way more efficient in a tight loop.
+
+  console.log('DEBUG777: %j', cartridges)
+  const small = cartridges[0]
+  const large = cartridges[1]
+
+  const largeDenom = large.denomination
+  const smallDenom = small.denomination
+  const largeBills = Math.min(large.count, Math.floor(amount / largeDenom))
+  const amountNum = amount.toNumber()
+
+  for (let i = largeBills; i >= 0; i--) {
+    const remainder = amountNum - largeDenom * i
+
+    if (remainder % smallDenom !== 0) continue
+
+    const smallCount = remainder / smallDenom
+    if (smallCount > small.count) continue
+
+    return [
+      {count: smallCount, denomination: small.denomination, id: uuid.v4()},
+      {count: i, denomination: largeDenom, id: uuid.v4()}
+    ]
+  }
+
+  return null
+}