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(require '[clojure.core.reducers :as r])
;(def target-area [[169 -68] [206 -108]])
(def target-area [[20000 -5000] [30000 -10000]])
;(def target-area [[2000 -500] [3000 -1000]])
(def initial-pos [0 0])
(defn beyond-target? [[[tbx tby] [tex tey]] [x y]]
(or (> x tex) (< y tey)))
(defn within-target? [[[tbx tby] [tex tey]] [x y]]
(and (>= x tbx) (<= x tex) (<= y tby) (>= y tey)))
(defn apply-velocity [[[px py] [vx vy]]]
[[(+ px vx) (+ py vy)] [(cond-> vx (pos? vx) dec) (dec vy)]])
(defn take-last-while [pred coll]
(loop [v (first coll) r (rest coll)]
(if (not (pred (first r)))
v
(recur (first r) (rest r)))))
(defn build-path [target vel]
(->> (iterate apply-velocity [initial-pos vel])
(take-last-while (comp not (partial beyond-target? target) first))
(first)))
; Used to determine best x velocity for highest path
(def tnum-seq (iterate #(do [(apply + %) (inc (second %))]) [0 1]))
(let [[tb te] target-area
lowest-x (second (last (take-while #(< (first %) (first tb)) tnum-seq)))
highest-y (dec (Math/abs (second te)))]
(->> (for [y (range (second te) (inc highest-y))
x (range lowest-x (inc (first te)))] [x y])
(#(do (println "Generated xy pairs...") %))
(#(do (println "Total: " (* (- highest-y (second te)) (- (inc highest-y) lowest-x))) %))
(partition 50000)
(#(do (println "Prepared partitions...") %))
(reduce
(fn [sum nlst]
(println sum)
(+ sum
(r/fold +
(r/monoid
(fn [tot xy]
(cond-> tot
(within-target? target-area (build-path target-area xy))
inc))
(constantly 0))
(into [] nlst))))
0)
(println)))
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