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lacolaco
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day12: The N-Body Problem
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‎resources/day12_input.txt‎

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<x=3, y=3, z=0>
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<x=4, y=-16, z=2>
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<x=-10, y=-6, z=5>
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<x=-3, y=0, z=-13>

‎src/clj_adventofcode_2019/day12.clj‎

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(ns clj-adventofcode-2019.day11
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(:require
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[clojure.java.io :as io]
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[clojure.math.numeric-tower :as math]
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[clojure.string :as str]))
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(defn parse-line [index line]
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[index { :pos
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(into {}
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(map (fn [[k v]] [(keyword k) (read-string v)])
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(map
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(fn [v] (str/split v #"="))
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(str/split (str/replace (str/replace line "<" "") ">" "") #", "))))
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:vel {:x 0 :y 0 :z 0}
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}])
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(def puzzle-input (slurp (io/resource "day12_input.txt")))
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(def initial-input
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(into {}
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(map-indexed parse-line (str/split-lines puzzle-input))))
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; initial-input
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; <x=-1, y=0, z=2>
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; <x=2, y=-10, z=-7>
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; <x=4, y=-8, z=8>
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; <x=3, y=5, z=-1>
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(def sample-moon-positions-1
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{0 {:pos {:x -1 :y 0 :z 2}
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:vel {:x 0 :y 0 :z 0}}
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1 {:pos {:x 2 :y -10 :z -7}
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:vel {:x 0 :y 0 :z 0}}
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2 {:pos {:x 4 :y -8 :z 8}
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:vel {:x 0 :y 0 :z 0}}
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3 {:pos {:x 3 :y 5 :z -1}
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:vel {:x 0 :y 0 :z 0}}})
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(defn adjust-all-axis [a b]
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(into {} (for [axis [:x :y :z]]
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[axis (+ (get a axis) (get b axis))])
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))
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(comment
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(adjust-all-axis {:x 0 :y 0 :z 10} {:x 5 :y -2 :z 0})
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;; => {:x 5, :y -2, :z 10}
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)
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(defn calc-vel [moon-index moons-data]
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(let [other-moons-data (filter (fn [[i _]] (not= i moon-index)) moons-data)
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other-moons-positions (map (fn [[_ data]] (:pos data)) other-moons-data)
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current-moon-pos (:pos (get moons-data moon-index))
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current-velocity (:vel (get moons-data moon-index))
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velocity-changes-grouped (group-by first (for [axis [:x :y :z]
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other-moon-pos other-moons-positions]
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(let [o (get other-moon-pos axis)
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c (get current-moon-pos axis)]
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(cond
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(= o c) [axis 0]
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(> o c) [axis 1]
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(< o c) [axis -1]))))
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velocity-changes-summed
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(into {}
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(map
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(fn [[axis v]] [axis (reduce + (map second v))])
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velocity-changes-grouped))
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new-velocity (adjust-all-axis current-velocity velocity-changes-summed)
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]
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new-velocity))
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(comment
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(calc-vel 3 sample-moon-positions-1)
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)
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(defn step [moons-data]
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(into {}
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(let [indexes (keys moons-data)]
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(for [index indexes]
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(let [new-velocity (calc-vel index moons-data)
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new-position (adjust-all-axis (:pos (get moons-data index)) new-velocity)]
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[index {:pos new-position :vel new-velocity}])))))
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(comment
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(step sample-moon-positions-1)
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;; => {0 {:pos {:x 2, :y -1, :z 1}, :vel {:x 3, :y -1, :z -1}},
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;; 1 {:pos {:x 3, :y -7, :z -4}, :vel {:x 1, :y 3, :z 3}},
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;; 2 {:pos {:x 1, :y -7, :z 5}, :vel {:x -3, :y 1, :z -3}},
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;; 3 {:pos {:x 2, :y 2, :z 0}, :vel {:x -1, :y -3, :z 1}}}
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(last (take 11 (iterate step sample-moon-positions-1)))
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;; => {0 {:pos {:x 2, :y 1, :z -3}, :vel {:x -3, :y -2, :z 1}},
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;; 1 {:pos {:x 1, :y -8, :z 0}, :vel {:x -1, :y 1, :z 3}},
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;; 2 {:pos {:x 3, :y -6, :z 1}, :vel {:x 3, :y 2, :z -3}},
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;; 3 {:pos {:x 2, :y 0, :z 4}, :vel {:x 1, :y -1, :z -1}}}
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)
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(defn energy [pos]
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(reduce + (map (fn [[_ v]] (math/abs v)) pos)))
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(defn total-energy [moon-data]
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(* (energy (:pos moon-data))
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(energy (:vel moon-data))))
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(comment
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(energy {:x 5 :y 1 :z -5})
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;; => 1
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(total-energy
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(get
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(last
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(take 11 (iterate step sample-moon-positions-1))) 0))
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;; => 36
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(map (fn [[_ moon-data]] (total-energy moon-data))
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(last (take 11 (iterate step sample-moon-positions-1))))
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;; => (36 45 80 18)
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(reduce +
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(map (fn [[_ moon-data]] (total-energy moon-data))
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(last (take 11 (iterate step sample-moon-positions-1)))))
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;; => 179
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)
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(step initial-input)
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;; => Execution error (NullPointerException) at clj-adventofcode-2019.day11/adjust-all-axis$iter$fn$fn (form-init7063701141190084591.clj:40).
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;; null
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;; => {0 {:x 3, :y 3, :z 0}, 1 {:x 4, :y -16, :z 2}, 2 {:x -10, :y -6, :z 5}, 3 {:x -3, :y 0, :z -13}}
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; part1 solution
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(reduce +
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(map (fn [[_ moon-data]] (total-energy moon-data))
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(last (take 1001 (iterate step initial-input)))))
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;; => 12351
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(defn does-history-really-repeat-itself [initial]
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(loop [tries 0
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input initial
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]
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(if (and (> tries 0) (= input initial)) {:tries tries :input input}
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(recur (inc tries) (step input)))
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))
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;; => #'clj-adventofcode-2019.day11/does-history-really-repeat-itself
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;; => #'clj-adventofcode-2019.day11/Does-history-really-repeat-itself
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(does-history-really-repeat-itself sample-moon-positions-1)
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;; => {:tries 2772,
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;; :input
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;; {0 {:pos {:x -1, :y 0, :z 2}, :vel {:x 0, :y 0, :z 0}},
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;; 1 {:pos {:x 2, :y -10, :z -7}, :vel {:x 0, :y 0, :z 0}},
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;; 2 {:pos {:x 4, :y -8, :z 8}, :vel {:x 0, :y 0, :z 0}},
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;; 3 {:pos {:x 3, :y 5, :z -1}, :vel {:x 0, :y 0, :z 0}}}}
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;;(does-history-really-repeat-itself initial-input)
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(defn get-axis [state axis]
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(map (fn [[i v]] [i {:pos (get (:pos v) axis)
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:vel (get (:vel v) axis)}]) state)
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)
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(get-axis initial-input :x)
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(defn does-history-really-repeat-itself-axis [initial axis]
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(loop [tries 0
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input initial]
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(if (and (> tries 0)
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(= (get-axis input axis) (get-axis initial axis)))
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{:tries tries :input input}
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(recur (inc tries) (step input)))))
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(does-history-really-repeat-itself-axis initial-input :x)
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;; => {:tries 22958,
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;; :input
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;; {0 {:pos {:x 3, :y 36, :z 582}, :vel {:x 0, :y 18, :z 6}},
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;; 1 {:pos {:x 4, :y -247, :z -85}, :vel {:x 0, :y -10, :z -1}},
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;; 2 {:pos {:x -10, :y 557, :z -300}, :vel {:x 0, :y -19, :z -2}},
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;; 3 {:pos {:x -3, :y -365, :z -203}, :vel {:x 0, :y 11, :z -3}}}}
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(does-history-really-repeat-itself-axis initial-input :y)
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;; => {:tries 286332,
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;; :input
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;; {0 {:pos {:x 4, :y 3, :z 137}, :vel {:x 9, :y 0, :z -3}},
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;; 1 {:pos {:x -2, :y -16, :z 156}, :vel {:x -4, :y 0, :z -59}},
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;; 2 {:pos {:x -18, :y -6, :z -308}, :vel {:x -15, :y 0, :z 37}},
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;; 3 {:pos {:x 10, :y 0, :z 9}, :vel {:x 10, :y 0, :z 25}}}}
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(does-history-really-repeat-itself-axis initial-input :z)
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;; => {:tries 231614,
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;; :input
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;; {0 {:pos {:x -85, :y 477, :z 0}, :vel {:x 12, :y 1, :z 0}},
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;; 1 {:pos {:x -10, :y -659, :z 2}, :vel {:x -5, :y 33, :z 0}},
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;; 2 {:pos {:x -5, :y 220, :z 5}, :vel {:x 8, :y -26, :z 0}},
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;; 3 {:pos {:x 94, :y -57, :z -13}, :vel {:x -15, :y -8, :z 0}}}}
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(defn gcd
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[a b]
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(if (zero? b)
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a
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(recur b, (mod a b))))
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(defn lcm
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[a b]
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(/ (* a b) (gcd a b)))
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(defn lcmv [& v] (reduce lcm v))
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; part2 solution
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(lcmv 231614 286332 22958)
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;; => 380635029877596

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