Feature/2018 day 13 part 2

2018/day-13/solution.js

@@ -13,7 +13,19 @@ const init = (data) => {
   const answer = [track.collision.x, track.collision.y]
   // console.log(`Track state:`)
   // console.log(track.display())
-  const answer2 = ''
+
+  // Execute again, this time, removing crashed carts instead of stopping
+  const track2 = new Track(data, { removeCrashedCarts: true })
+  while (track2.carts.length > 1) {
+    track2.advance()
+  }
+
+  // console.log(track2.display())
+  const remaining = track2.carts[0]
+  // console.log(`${remaining.length} cart(s) of ${track2.carts.length} remaining at frame ${track2.frame}`)
+  // console.log(remaining)
+  const answer2 = [remaining.x, remaining.y]
+
   console.log(`-- Part 1 --`)
   console.log(`Answer: ${answer}`)
   console.log(`-- Part 2 --`)

2018/day-13/tracks.js

@@ -1,13 +1,16 @@
 const { dynamicSortMultiple } = require('../day-04/helpers')
 
 class Track {
-  constructor (track) {
+  constructor (track, options) {
     this.layout = []
     this.carts = []
     this.cartDirections = ['^', '>', 'v', '<']
     this.collision = false
     this.frame = 0
     this.interSectionOrder = [-1, 0, 1]
+    this.options = options || {
+      removeCrashedCarts: false
+    }
     this.trackTurns = ['\\', '/']
     this.trackTypes = this.trackTurns.concat(['-', '|', '+'])
     this.setLayout(track)
@@ -81,14 +84,16 @@ class Track {
    */
   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)
-      }
-    })
+    while (this.carts.filter((c) => c.moved === this.frame).length < this.carts.length) {
+      this.carts.filter((c) => c.moved !== this.frame).sort(dynamicSortMultiple('y', 'x')).forEach((c) => {
+        try {
+          this.moveCart(c)
+        } catch (err) {
+          console.error(`Problem moving cart in frame ${this.frame}`)
+          console.error(err)
+        }
+      })
+    }
   }
 
   /**
@@ -157,6 +162,7 @@ class Track {
     const l = (d % 3 === 0) ? -1 : 1 // (+/-) distance of travel on the axis
     // move the cart
     cart[a] = cart[a] + l
+    cart.moved = this.frame
     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
@@ -166,17 +172,28 @@ class Track {
     // Check for collision
     if (this._isCollision(cart.x, cart.y)) {
       this.collision = { x: cart.x, y: cart.y }
-      throw new Error(`collision at ${cart.x}, ${cart.y}`) // Stop everything
+      console.log(`Collision in frame ${this.frame}. removeCrashedCarts is ${this.options.removeCrashedCarts}`)
+
+      // Handle crashed carts
+      if (this.options.removeCrashedCarts) {
+        this.carts.filter((c) => c.x === cart.x && c.y === cart.y).forEach((c) => {
+          this.carts.splice(this.carts.indexOf(c), 1)
+        })
+      } else {
+        throw new Error(`collision at ${cart.x}, ${cart.y}`) // Stop everything
+      }
     }
+
     // rotate the cart when entering a turn
     if (this._isTurn(s)) {
       cart.direction = this._rotate(s, a, d)
-      return
+      return true
     }
     // rotate (or not) the cart when entering an intersection
     if (this._isIntersection(s)) {
       cart.direction = this._intersect(cart)
     }
+    return true
   }
 
   /**

2018/day-13/tracks.test.js

@@ -201,4 +201,33 @@ describe('--- Day 13: Mine Cart Madness ---', () => {
       })
     })
   })
+  describe('Part 2:', () => {
+    describe('new Track(layout, options)', () => {
+      it('removes crashed carts when enabled', () => {
+        const testData = `/>-<\\
+|   |
+| /<+-\\
+| | | v
+\\>+</ |
+  |   ^
+  \\<->/`
+        const expected = `/---\\
+|   |
+| /-+-\\
+| | | |
+\\-+-/ ^
+  |   |
+  \\---/`.trim()
+        const track = new Track(testData, { removeCrashedCarts: true })
+        while (track.carts.length > 1) {
+          track.advance()
+        }
+        const actual = track.display().trim()
+        expect(actual).to.equal(expected)
+        expect(track.carts[0].x).to.equal(6)
+        expect(track.carts[0].y).to.equal(4)
+        expect(track.frame).to.equal(3)
+      })
+    })
+  })
 })