fix: allow makeChange to balance out cassettes

lib/bill-math.js

@@ -1,5 +1,5 @@
 const uuid = require('uuid')
-const _ = require('lodash')
+const _ = require('lodash/fp')
 
 // 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.
@@ -63,11 +63,12 @@ function makeChangeDynamic (cassettes, amount) {
     ) {
       if (cassettes[1].denomination === 0) break
       if (
-        i * cassettes[0].denomination +
+        i * cassettes[0].denomination + j * cassettes[1].denomination ===
-          j * cassettes[1].denomination ===
           amountNum &&
         i <= cassettes[0].count &&
-        j <= cassettes[1].count && i >= 0 && j >= 0
+        j <= cassettes[1].count &&
+        i >= 0 &&
+        j >= 0
       ) {
         solutions.push([
           {
@@ -108,7 +109,10 @@ function makeChangeDynamic (cassettes, amount) {
             amountNum &&
           i <= cassettes[0].count &&
           j <= cassettes[1].count &&
-          k <= cassettes[2].count && i >= 0 && j >= 0 && k >= 0
+          k <= cassettes[2].count &&
+          i >= 0 &&
+          j >= 0 &&
+          k >= 0
         ) {
           solutions.push([
             {
@@ -152,7 +156,11 @@ function makeChangeDynamic (cassettes, amount) {
             i <= cassettes[0].count &&
             j <= cassettes[1].count &&
             k <= cassettes[2].count &&
-            l <= cassettes[3].count && i >= 0 && j >= 0 && k >= 0 && l >= 0
+            l <= cassettes[3].count &&
+            i >= 0 &&
+            j >= 0 &&
+            k >= 0 &&
+            l >= 0
           ) {
             solutions.push([
               {
@@ -182,11 +190,21 @@ function makeChangeDynamic (cassettes, amount) {
     }
   }
 
-  const sortedSolutions = _.sortBy(solutions, it => {
+  const sortedSolutions = _.sortBy(it => {
-    _.reduce(it, (acc, value) => acc + value.provisioned, 0)
+    const arr = []
-  })
 
-  const cleanSolution = _.filter(_.head(sortedSolutions), it => it.denomination > 0)
+    for (let la = 0; la < 4; la++) {
+      arr.push(cassettes[la].count - it[la].provisioned)
+    }
+
+    if (arr.length < 2) return Infinity
+    return _.max(arr) - _.min(arr)
+  }, solutions)
+
+  const cleanSolution = _.filter(
+    it => it.denomination > 0,
+    _.head(sortedSolutions)
+  )
 
   return cleanSolution
 }