fix(2020-day-12): ferry could fail when rotated more than 360 degrees

Author: developher-net

2020/day-12/ferry.js

@@ -30,10 +30,18 @@ const move = ({
     L: (u) => { // Turn Left
       position.d -= u
       position.d = position.d % 360
+      // prevent negative angles
+      if (position.d < 0) {
+        position.d += 360
+      }
     },
     R: (u) => { // Turn Right
       position.d += u
       position.d = position.d % 360
+      // prevent negative angles
+      if (position.d < 0) {
+        position.d += 360
+      }
     },
     F: (u) => { // Forward
       // TODO: replace with vector positioning of arbitrary angles

2020/day-12/ferry.test.js

@@ -75,6 +75,12 @@ describe('--- Day 11: Seating System ---', () => {
         expect(move({ command: 'F10' }))
           .to.deep.equal({ x: 10, y: 0, d: 90 })
       })
+      it('can be rotated more than 360 degrees', () => {
+        expect(move({ command: 'L720' }))
+          .to.deep.equal({ x: 0, y: 0, d: 90 })
+        expect(move({ position: { x: 0, y: 0, d: -810 }, command: 'R720' }))
+          .to.deep.equal({ x: 0, y: 0, d: 270 })
+      })
     })
     describe('route()', () => {
       it('can follow a list of instructions', () => {