perf(2020-day-13): speed up search by exiting out of times as soon as there is a mismatch

Author: developher-net

2020/day-13/busSchedules.js

@@ -28,10 +28,19 @@ const findSequentialTime = (schedule) => {
   // If we get an array the same length as the routes array, that means all routes matched
   while (result.length < routes.length) {
     x += routes[0]
-    result = routes.filter((route, idx) => {
-      if (route === 'x') { return true } // x doesn't matter
-      return ((x + idx) % route === 0) // Route is sequentially +1 above the previous route
-    })
+    // loop through the list looking for el mod = idx
+    let matches = true
+    let i = 0
+    while (i < routes.length && matches === true) {
+      if (routes[i] === 'x') { // "x" doesn't matter
+        i++
+      } else if ((x + i) % routes[i] === 0) { // Route is sequentially +1 above the previous route
+        i++
+      } else {
+        matches = false
+      }
+    }
+    if (matches) { result = routes }
   }
   console.debug(`Found a match ${x}`)
   return x

2020/day-13/busSchedules.test.js

@@ -30,7 +30,7 @@ describe('--- Day 13: Shuttle Search ---', () => {
   describe('Part 2', () => {
     describe('findSequentialTime', () => {
       it('finds a sequential time where the busses all depart sequentially', () => {
-        // expect(findSequentialTime('7,13,x,x,59,x,31,19')).to.equal(1068781)
+        expect(findSequentialTime('7,13,x,x,59,x,31,19')).to.equal(1068781)
         expect(findSequentialTime('17,x,13,19')).to.equal(3417)
         expect(findSequentialTime('67,7,59,61')).to.equal(754018)
         expect(findSequentialTime('67,x,7,59,61')).to.equal(779210)