feat(2018 day-13): advance all carts each turn and correctly handle intersection rotation logic

Author: developher-net

2018/day-13/solution.js

@@ -2,15 +2,18 @@ const {
   Track
 } = require('./tracks')
 
-/* eslint-disable */
 const data = `/->-\\
 |   |  /----\\
 | /-+--+-\\  |
 | | |  | v  |
 \\-+-/  \\-+--/
   \\------/   `
-/* eslint-enable */
 
-const mytrack = new Track(data)
-const actual = mytrack.display()
-console.log(actual)
+const track = new Track(data)
+while (track.collision === false) {
+  track.advance()
+}
+
+console.error(`Reached a collision at ${track.collision.x},${track.collision.y} on frame ${track.frame}`)
+console.log(`Track state:`)
+console.log(track.display())

2018/day-13/tracks.js

@@ -1,12 +1,14 @@
+const { dynamicSortMultiple } = require('../day-04/helpers')
+
 class Track {
   constructor (track) {
     this.layout = []
     this.carts = []
     this.cartDirections = ['^', '>', 'v', '<']
-    this.trackTurns = ['\\', '/']
-    this.trackTypes = this.trackTurns.concat(['-', '|', '+'])
     this.collision = false
     this.frame = 0
+    this.trackTurns = ['\\', '/']
+    this.trackTypes = this.trackTurns.concat(['-', '|', '+'])
     this.setLayout(track)
   }
 
@@ -16,21 +18,18 @@ class Track {
 
   /**
    * Determines the next direction for a cart rotating at an intersection
-   * Order of rotations is left (counterclockwise), right (clockwise), straight
+   * Order of rotations is left (counterclockwise), straigh, right (clockwise), straight
    * @private
    * @param {Object} cart the cart being turned
    * @returns {String} value of new direction
    */
   _intersect (cart) {
-    let r = 0
-    if (typeof cart.lastIntersection === 'undefined') {
-      r = -1
-    }
-    if (cart.lastIntersection === -1) {
-      r = 1
-    }
+    let l = cart.lastIntersections
+    let r = (l[0] !== 0) ? 0 : l[1] * -1
+    // Track the intersections
+    cart.lastIntersections.pop()
+    cart.lastIntersections.splice(0, 0, r)
 
-    cart.lastIntersection = r
     return this.cartDirections[this._roationDirection(this.cartDirections.indexOf(cart.direction), r)]
   }
 
@@ -50,7 +49,6 @@ class Track {
       // (this.trackTurns.indexOf(s) === 0 && a === 'x') // horizontal turns counter-clockwise
       // (this.trackTurns.indexOf(s) === 1 && a === 'y') // vertical turns counter-clockwise
     ) ? 1 : -1
-    console.log(`${s} for ${a} is turning ${r}`)
     // Find the value of the new direction
     return this.cartDirections[this._roationDirection(d, r)]
   }
@@ -63,17 +61,30 @@ class Track {
    * @returns {Number} Index of new direction
    */
   _roationDirection (d, r) {
-    console.log(`rotating ${d}, ${r}`)
     if (d + r > this.cartDirections.length - 1) {
       return 0
     }
     if (d + r < 0) {
       return this.cartDirections.length - 1
     }
-    console.log(`new direction is ${d + r}`)
     return d + r
   }
 
+  /**
+   * Advances the state of the entire layout
+   */
+  advance () {
+    this.frame++
+    this.carts.sort(dynamicSortMultiple('y', 'x')).forEach((c) => {
+      try {
+        this.moveCart(c)
+      } catch (err) {
+        console.error(`Problem moving cart in frame ${this.frame}`)
+        console.error(err)
+      }
+    })
+  }
+
   /**
    * Displays the current state of the track with the carts placed
    */
@@ -108,7 +119,8 @@ class Track {
           this.carts.push({
             x: idx,
             y: idy,
-            direction: x
+            direction: x,
+            lastIntersections: [0, 1] // Assume the first intersection the cart will turn left
           })
           // Replace the cart on the track with a track segment
           // (Assuming cart initial states aren't on instersections)
@@ -124,7 +136,7 @@ class Track {
    * @param {*} x Number
    * @param {*} y Number
    */
-  getSegmentType (x, y) {
+  getSegment (x, y) {
     return this.layout[y][x]
   }
 
@@ -139,22 +151,20 @@ class Track {
     const l = (d % 3 === 0) ? -1 : 1 // (+/-) distance of travel on the axis
     // move the cart
     cart[a] = cart[a] + l
-    const s = this.layout[cart.y][cart.x] // Segment of track the cart is now on
+    const s = this.getSegment(cart.x, cart.y) // Segment of track the cart is now on
 
     // Make sure cart hasn't run off the rails
     if (this.trackTypes.indexOf(this.layout[cart.y][cart.x]) < 0) {
-      return new Error(`cart ran off the track at ${cart.x}, ${cart.y}`)
+      throw new Error(`cart ran off the track at ${cart.x}, ${cart.y}`)
     }
     // Check for collision
     if (this._isCollision(cart.x, cart.y)) {
       this.collision = { x: cart.x, y: cart.y }
-      return new Error(`collision at ${cart.x}, ${cart.y}`) // Stop everything
+      throw new Error(`collision at ${cart.x}, ${cart.y}`) // Stop everything
     }
     // rotate the cart when entering a turn
     if (this._isTurn(s)) {
-      console.log(`Cart direction was ${cart.direction}`)
       cart.direction = this._rotate(s, a, d)
-      console.log(`Cart direction is ${cart.direction}`)
       return
     }
     // rotate (or not) the cart when entering an intersection

2018/day-13/tracks.test.js

@@ -22,11 +22,13 @@ describe('--- Day 13: Mine Cart Madness ---', () => {
         const expected = [{
           x: 2,
           y: 0,
-          direction: '>'
+          direction: '>',
+          lastIntersections: [0, 1]
         }, {
           x: 9,
           y: 3,
-          direction: 'v'
+          direction: 'v',
+          lastIntersections: [0, 1]
         }]
         const track = new Track(data)
         const actual = track.carts
@@ -35,22 +37,23 @@ describe('--- Day 13: Mine Cart Madness ---', () => {
     })
     describe('advance()', () => {
       it('moves forward all carts on the layout', () => {
-        const test = `/---v
+        const test = `/---\\
 |   |  /----\\
-| /-+--+-\\  |
-| | |  | |  |
-\\-+-/  \\-+>-/
+| /-+>-+-\\  |
+| | |  | |  ^
+\\-+-/  \\-+--/
   \\------/   `
-        const expected = `/---\
-|   v  /----\\
-| /-+--+-\\  |
+        const expected = `/---\\
+|   |  /----\\
+| /-+->+-\\  ^
 | | |  | |  |
-\\-+-/  \\-+->/
+\\-+-/  \\-+--/
   \\------/   `.trim()
         const track = new Track(test)
-        track.moveCart()
+        track.advance()
         const actual = track.display()
         expect(actual).to.equal(expected)
+        expect(track.frame).to.equal(1)
       })
     })
     describe('moveCart(cart)', () => {
@@ -124,19 +127,26 @@ describe('--- Day 13: Mine Cart Madness ---', () => {
         const actual = track.display()
         expect(actual).to.equal(expected)
       })
-      it('tracks the direction through multiple intersections following the sequential rotation rules: left, straight, right', () => {
-        const test = `
+      it('tracks the direction through multiple intersections following the sequential rotation rules: left, straight, right, straight', () => {
+        const expected = `
+       ^
+       |
+   +-+-+
    |
-  -+-+--
+   +
    |
-->-+-`
-        const track = new Track(test)
-        const expected = `
+---+`.trim()
+        const test = `
+       |
+       |
+   +-+-+
    |
-  -+-+->
+   +
    |
----+-`.trim()
-        for (let i = 0; i < 8; i++) {
+->-+`
+        const track = new Track(test)
+
+        for (let i = 0; i < 12; i++) {
           track.moveCart(track.carts[0])
         }
         const actual = track.display()
@@ -154,18 +164,24 @@ describe('--- Day 13: Mine Cart Madness ---', () => {
       it('throws an error if the cart runs off the rails', () => {
         const test = `->- -`
         const track = new Track(test)
-        track.moveCart(track.carts[0])
-        expect(track.moveCart(track.carts[0])).to.be.an('error')
+        try {
+          track.moveCart(track.carts[0])
+        } catch (err) {
+          expect(err).to.be.an('error')
+        }
       })
       it('registers a collision', () => {
         const test = `->-<-`
         const expected = `---X-`
         const track = new Track(test)
-        track.moveCart(track.carts[0])
-        track.moveCart(track.carts[0])
-        const actual = track.display()
-        expect(actual).to.equal(expected)
-        expect(track.collision).to.deep.equal({ x: 3, y: 0 })
+        try {
+          track.moveCart(track.carts[0])
+          track.moveCart(track.carts[0])
+        } catch (err) {
+          const actual = track.display()
+          expect(actual).to.equal(expected)
+          expect(track.collision).to.deep.equal({ x: 3, y: 0 })
+        }
       })
     })
     describe('display()', () => {
@@ -176,11 +192,11 @@ describe('--- Day 13: Mine Cart Madness ---', () => {
         expect(actual).to.equal(expected)
       })
     })
-    describe('getSegmentType(x,y)', () => {
+    describe('getSegment(x,y)', () => {
       it('queries the type of segment at location x,y', () => {
         const expected = '-'
         const track = new Track(data)
-        const actual = track.getSegmentType(5, 2)
+        const actual = track.getSegment(5, 2)
         expect(actual).to.equal(expected)
       })
     })