feat(2020-day-10): tally up the voltage differences across the set of adapters

Author: developher-net

2020/day-10/jolts.js

@@ -1,8 +1,29 @@
 const countDifferences = (data) => {
-  if (data.length > 15) {
-    return [0, 22, 0, 10]
-  }
-  return [0, 7, 0, 5]
+  const tallies = Array(4).fill(0)
+  // Always account for the outlet
+  data.push(0)
+  // Always add the native adapter at the end
+  tallies[3]++
+
+  // Iterate through the adapters
+  data.sort((a, b) => a - b)
+    .forEach((curr, idx) => {
+      if (!data[idx + 1]) {
+        // end of array, nothing to do
+        return
+      }
+      const next = data[idx + 1]
+      const delta = next - curr
+      if (delta > 3) {
+        // Problem with data. Gap in joltages greater than allowed
+        throw new Error(`Joltage difference between ${curr} and ${next} is greater than allowed.`)
+      }
+
+      console.debug(`Joltage difference between ${curr} and ${next} is ${delta}.`)
+      tallies[delta]++
+    })
+
+  return tallies
 }
 
 module.exports = {

2020/day-10/jolts.test.js

@@ -18,6 +18,9 @@ describe('--- Day 10: Adapter Array ---', () => {
         expect(result2[1]).to.equal(22)
         expect(result2[3]).to.equal(10)
       })
+      it('throws an error if any joltage differences exceed 3', () => {
+        expect(() => countDifferences([5, 40])).to.throw()
+      })
     })
   })
 })