feat: makeChange function supporting multiple cassettes

lib/bill-math.js

@@ -1,4 +1,5 @@
 const uuid = require('uuid')
+const _ = require('lodash')
 
 // 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.
@@ -10,28 +11,37 @@ exports.makeChange = function makeChange (cassettes, 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.
-
-  const small = cassettes[0]
-  const large = cassettes[1]
-
-  const largeDenom = large.denomination
-  const smallDenom = small.denomination
-  const largeBills = Math.min(large.count, Math.floor(amount / largeDenom))
+  const cassetteMap = _.map(cassettes, it => ({
+    denomination: it.denomination
+  }))
   const amountNum = amount.toNumber()
 
-  for (let i = largeBills; i >= 0; i--) {
-    const remainder = amountNum - largeDenom * i
+  const sortedCassettes = _.orderBy(cassetteMap, ['denomination'], ['desc'])
 
-    if (remainder % smallDenom !== 0) continue
+  const finalDist = []
 
-    const smallCount = remainder / smallDenom
-    if (smallCount > small.count) continue
+  let mutableAmount = _.clone(amountNum)
 
-    return [
-      {provisioned: smallCount, denomination: small.denomination, id: uuid.v4()},
-      {provisioned: i, denomination: largeDenom, id: uuid.v4()}
-    ]
+  while(mutableAmount >= 0) {
+    _.each(sortedCassettes, it => {
+      if (mutableAmount === 0) {
+        finalDist.push({provisioned: 0, denomination: it.denomination, id: uuid.v4()})
+        return
+      }
+
+      const remainder = mutableAmount % it.denomination
+      const amountToSub = mutableAmount - remainder
+      const numberOfBills = amountToSub / it.denomination
+      mutableAmount -= amountToSub
+
+      finalDist.push({provisioned: numberOfBills, denomination: it.denomination, id: uuid.v4()})
+      return
+    })
+
+    if (mutableAmount === 0) {
+      break
+    }
   }
 
-  return null
+  return finalDist
 }