Index: day15.rkt
==================================================================
--- day15.rkt
+++ day15.rkt
@@ -8,36 +8,58 @@
threading)
;; Good ol’ positions.
(struct posn (x y) #:transparent)
-;; The concept of “reading order” is an important one in this puzzle. We can use
-;; this comparison function with `sort` to ensure a list of positions is sorted
-;; according to how you’d encounter them reading left-to-right, top to bottom.
-;; This is where I mention that this program views 0,0 as “top left”.
+;; The concept of “reading order” is an important one in this puzzle. Fighters move,
+;; targets and paths are chosen in order of how you’d encounter them reading the grid
+;; left-to-right, top to bottom.
+;; The two functions below are going to do all the work of determining sort order
+;; for us, whenever we need it.
+;; This is also where I mention that this program views 0,0 as “top left”.
(define (posn<? p1 p2)
(match-define (posn x1 y1) p1)
(match-define (posn x2 y2) p2)
(or (< y1 y2)
(and (<= y1 y2)
(<= x1 x2))))
+(define (reading-order lst)
+ (sort lst posn<?))
+
+(define (posn=? p1 p2)
+ (and (equal? (posn-x p1) (posn-x p2))
+ (equal? (posn-y p1) (posn-y p2))))
+
;; Keeping track of elves and gnomes. We’ll have separate lists for each group.
;; Making this a subtype of posn means we can pass a fighter to any function
;; that expects a posn.
-(struct fighter (hp) #:super struct:posn #:transparent)
+(struct fighter (type hp) #:super struct:posn #:transparent)
+(define ATTACK-POWER 3)
+(define STARTING-HP 200)
;; “The grid…a digital frontier. I tried to picture clusters of information as
;; they moved through the computer. What did they look like? …I kept dreaming
;; of a world I thought I’d never see. And then one day…I got in.”
;; https://youtu.be/QBYr0k8dOtw?t=24
-(struct grid (vec rows cols) #:transparent)
;; Our “grid” is, behind the scenes, a one-dimensional vector with length ROWS*COLS.
-;; This function translates an x,y pair
-(define (coords->index g x y)
- (+ (* (grid-cols g) y) x))
+;; The “target” tracks the end-point of the path the grid describes (when used as a
+;; “path map”, see below
+(struct grid (vec rows cols start target) #:transparent)
+
+;; Translate between an x,y pair of coordinates and an index into the grid vector
+(define (posn→index g p)
+ (+ (* (grid-cols g) (posn-y p)) (posn-x p)))
+
+(define (index→posn g i)
+ (posn (modulo i (grid-cols g))
+ (quotient i (grid-cols g))))
+
+;; This will come in handy later.
+;; A path-step is a sub-type of posn with
+(struct path-step (dist) #:super struct:posn #:transparent)
;; Create a grid from a list of strings each representing a row, filling each
;; spot with the corresponding character in the string
(define (lines->grid line-strs)
(define row-count (length line-strs))
@@ -44,11 +66,13 @@
(define col-count (string-length (first line-strs)))
(grid (apply vector-append
(map list->vector
(map string->list line-strs)))
row-count
- col-count))
+ col-count
+ #f
+ #f))
(define test-map
(lines->grid
'("#######"
"#E..G.#"
@@ -58,28 +82,26 @@
;; Grids and Positions: put them together
;; Reference the value at given position in a grid
(define (grid-ref g p)
- (match-define (posn x y) p)
- (vector-ref (grid-vec g) (coords->index g x y)))
+ (vector-ref (grid-vec g) (posn→index g p)))
;; Change the value at given position
(define (grid-mark! g pos v)
- (match-define (posn x y) pos)
- (vector-set! (grid-vec g) (coords->index g x y) v))
+ (vector-set! (grid-vec g) (posn→index g pos) v))
;; Used to determine if a fighter could move into a given spot.
;; Anything besides "." counts as an obstruction (incl. other fighters)
(define (grid-clear-at? g p)
(equal? (grid-ref g p) #\.))
;; Make a blank grid of the same dimensions, for use in making “path grids” (see
;; further below)
-(define (copy-blank-grid g)
- (match-define (grid _ rows cols) g)
- (grid (make-vector (* rows cols) #f) rows cols))
+(define (copy-blank-grid g [start #f] [target #f])
+ (match-define (grid _ rows cols _) g)
+ (grid (make-vector (* rows cols) #f) rows cols start target))
;; (For debugging) Represent the grid as a square of single-character values
(define (display-grid g [g2 #f])
(define grid-size (* (grid-cols g) (grid-rows g)))
(display
@@ -116,11 +138,11 @@
(posn x (- y 1)))))
;; Get all the EMPTY neighboring points of a given spot OR list of spots.
;; If a (listof posn?) is passed, ensures the returned list does not include
;; any of the original positions.
-(define (free-neighbors-at world pos)
+(define (free-neighbors-of world pos)
(cond [(posn? pos)
(~> (neighbor-coords world pos)
(filter (curry grid-clear-at? world) _))]
[(list? pos)
(~> (map (curry neighbor-coords world) pos)
@@ -135,18 +157,86 @@
(define (not-yet-checked? pmap pos)
(not (grid-ref pmap pos)))
;; Find the most direct path(s) to a fighter from an end-position
(define (path-grid world f end-pos)
- (define result-grid (copy-blank-grid world))
- (define goal-pts (free-neighbors-at world f))
+ (define result-grid (copy-blank-grid world f end-pos))
+ (define goal-pts (free-neighbors-of world f))
(grid-mark! result-grid end-pos 0)
(let loop ([pts-to-check (list end-pos)]
[i 1])
- (define new-coords (~> (free-neighbors-at world pts-to-check)
+ (define new-coords (~> (free-neighbors-of world pts-to-check)
(filter (curry not-yet-checked? result-grid) _)))
(for-each (lambda (p) (grid-mark! result-grid p i)) new-coords)
(cond
[(not (empty? (set-intersect new-coords goal-pts))) result-grid]
[(empty? new-coords) #f]
[else (loop new-coords (+ 1 i))])))
+
+;; What is the distance of the path represented by a path-map?
+(define (path-distance pmap)
+ (~>> (neighbor-coords pmap (grid-start pmap))
+ (filter-map (curry grid-ref pmap)) ; Weeds out #f values
+ (apply min)))
+
+;; Get only the shortest path(s) from a list of path maps
+(define (shortest plst)
+ (define shortest-distance (apply min (map (curry path-distance f) plst)))
+ (define (among-shortest? pmap) (equal? shortest-distance (path-distance pmap)))
+ (filter among-shortest? plst))
+
+;; What is the actual next step a fighter should take along a particular path,
+;; breaking ties by reading order?
+(define (next-step pmap f)
+ (define (coord→step c) (cond [c (path-step (posn-x c) (posn-y c) (grid-ref pmap c))] [else #f]))
+ (define possibles
+ (~>> (neighbor-coords f)
+ (filter-map coord→step)))
+ (define min-dist (min (map path-step-dist possibles)))
+ (~>> (filter (λ (ps) (equal? min-dist (path-step-dist ps))) possibles)
+ reading-order
+ first))
+
+
+
+;;
+;; Let’s start doing stuff with fighters
+
+;; Make a list of fighters from a grid, with the results in reading order.
+(define (grid->fighters g)
+ (for/fold ([fighters '()]
+ #:result (reading-order fighters))
+ ([val (in-vector (grid-vec g))]
+ [idx (in-naturals)])
+ (cond [(member val '(#\G #\E))
+ (match-define (posn x y) (index→posn g idx))
+ (cons (fighter x y val STARTING-HP) fighters)]
+ [else fighters])))
+
+(define (fighter-located-in? f lst)
+ (not (empty? (filter (curry posn=? f) lst))))
+
+(define (enemies? f1 f2)
+ (not (equal? (fighter-type f1) (fighter-type f2))))
+
+(define (enemies-of f1 flst)
+ (filter (curry enemies? f1) flst))
+
+(define (adjacent-enemies world f all-enemies)
+ (define adjacent-posns (neighbor-coords world f))
+ (filter (curryr fighter-located-in? adjacent-posns) all-enemies))
+
+(define (fighter-alive? f)
+ (positive? (fighter-hp f)))
+
+(define (determine-next-move world f enemies)
+ #t)
+
+(define fs (grid->fighters test-map))
+(define f (first fs))
+(define es (enemies-of f fs))
+(define possible-targets (free-neighbors-of test-map es))
+(define possible-paths (filter-map (curry path-grid test-map f) possible-targets))
+
+
+