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(ns tractmanager.lockscreengist)
(def stride 3)
(defn distance
"returns [deltaX deltaY]"
[[x1 y1] [x2 y2]]
[(- x2 x1) (- y2 y1)])
(defn coordinates
"returns the coordinate of the supplied index"
[index stride]
(let [fixed-index (- index 1)]
[(mod fixed-index stride) (int (/ fixed-index stride))]))
(defn add-to-element
"adds a value to an element at an index and returns the resulting collection"
[coll index value]
(assoc coll index (+ (nth coll index) value)))
(defn neighbors
"returns the neighbors in an axis"
[coord index]
(->> (range -1 2)
(map (partial add-to-element coord index))))
(defn out-of-bounds?
"checks if the index is outside of the range of our screen array"
[stride coord]
(some #(or (<= stride %) (neg? %)) coord))
(defn around
"returns the elements around the index"
[stride coord]
(->> coord
(#(neighbors % 0))
(mapcat #(neighbors % 1))
(filter (comp not (partial out-of-bounds? stride)))))
(defn get-index
"returns the index of a supplied coordinate"
(if (nil? coord)
(+ (first coord) (* (second coord) stride))))
(defn knight-neighbors
"returns the neighbors that can be reached via a knights jump"
(let [offsets (for [x [-1 1]
y [2 -2]]
(vector x y))
offsets (apply concat [offsets (mapv reverse offsets)])]
(->> offsets
(map (partial map + coord))
(filter (comp not (partial out-of-bounds? stride)))
(map get-index)
(map (partial + 1)))))
(defn targetables
"returns the valid moves around the starting point"
(let [coord (coordinates number stride)]
(->> coord
(around stride)
(map get-index)
(mapv (partial + 1))
(concat (knight-neighbors coord)))))
(defn calculate-intermediate
"calculates the position between start and end in a 2D array"
[start end]
(let [start-coord (coordinates start stride)
end-coord (coordinates end stride)
dist (distance start-coord end-coord)]
(->> dist
(map #(/ % 2))
(map-indexed (fn [idx itm] (+ (nth start-coord idx) itm)))
(+ 1))))
(defn valid-move
"checks if a move is valid given a list of previous moves and a start/end"
[prev start end]
(if (some #{end} prev)
(let [available (targetables start)]
(if (some #{end} available)
(let [intermediate (calculate-intermediate start end)]
(some #{intermediate} prev))))))
(defn valid-path
"checks to see if a path is valid by recursively stepping through the path and checking against its history"
(loop [remaining (rest path)
previous [(first path)]]
(let [next (first remaining)
last (last previous)]
(if (nil? next) true
(if (valid-move previous last next)
(recur (rest remaining)
(conj previous (first remaining)))
(assert (true? (valid-path [1 6 7 4])))
(assert (true? (valid-path [2 1 3])))
(assert (false? (valid-path [1 9])))
(assert (false? (valid-path [1 2 3 2 1])))
(assert (false? (valid-path [0 1 2 3])))
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