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60 lines
1.9 KiB
CCo�jrr
60 lines
1.9 KiB
CCo�jrr
3 years ago
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; Put into a lein project so that you can pass Java more RAM (e.g. -Xmx15G)
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; https://www.reddit.com/r/adventofcode/comments/riqtwx/2021_day_17_day_17_part_3/
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;
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;
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(require '[clojure.core.reducers :as r])
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(def target-area [[20000 -5000] [30000 -10000]])
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(def initial-pos [0 0])
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(defn beyond-target? [[[tbx tby] [tex tey]] [x y]]
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(or (> x tex) (< y tey)))
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(defn within-target? [[[tbx tby] [tex tey]] [x y]]
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(and (>= x tbx) (<= x tex) (<= y tby) (>= y tey)))
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(defn apply-velocity [[[px py] [vx vy]]]
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[[(+ px vx) (+ py vy)] [(cond-> vx (pos? vx) dec) (dec vy)]])
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(defn take-last-while [pred coll]
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(loop [v (first coll) r (rest coll)]
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(if (not (pred (first r)))
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v
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(recur (first r) (rest r)))))
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(defn build-path [target vel]
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(->> (iterate apply-velocity [initial-pos vel])
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(take-last-while (comp not (partial beyond-target? target) first))
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(first)))
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; Used to determine best x velocity for highest path
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(def tnum-seq (iterate #(do [(apply + %) (inc (second %))]) [0 1]))
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(let [[tb te] target-area
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lowest-x (second (last (take-while #(< (first %) (first tb)) tnum-seq)))
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highest-y (dec (Math/abs (second te)))]
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(->> (for [y (range (second te) (inc highest-y))
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x (range lowest-x (inc (first te)))] [x y])
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(#(do (println "Generated xy pairs...") %))
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(#(do (println "Total: " (* (- highest-y (second te)) (- (inc highest-y) lowest-x))) %))
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(partition 1000000)
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(#(do (println "Prepared partitions...") %))
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(reduce
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(fn [sum nlst]
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(println sum)
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(+ sum
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(r/fold +
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(r/monoid
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(fn [tot xy]
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(cond-> tot
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(within-target? target-area (build-path target-area xy))
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inc))
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(constantly 0))
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(into [] nlst))))
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0)
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(println)))
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