add day 17

diff --git a/day17/part1.clj b/day17/part1.clj
new file mode 100644 (file)
index 0000000..220e408
--- /dev/null
+++ b/day17/part1.clj
@@ -0,0 +1,34 @@
+(def target-area [[169 -8] [206 -108]])
+;(def target-area [[20 -5] [30 -10]])
+(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 [[pos vel]]
+  [[(+ (first pos) (first vel)) (+ (second pos) (second vel))]
+   [(cond-> (first vel) (> (first vel) 0) dec (< (first vel) 0) inc) (dec (second vel))]])
+
+(defn path-builder [vel] (iterate apply-velocity [initial-pos vel]))
+
+(defn build-path [target vel]
+  (map first
+    (take-while (comp not (partial beyond-target? target) first)
+                (path-builder vel))))
+
+(defn path-height [target vel]
+  (let [path (build-path target vel)]
+    (when (within-target? target (last path))
+      (apply max (map second path)))))
+
+(def tnum-seq (iterate #(do [(+ (first %) (second %)) (inc (second %))]) [0 1]))
+
+(let [x (second (last (take-while #(< (first %) (first (first target-area))) tnum-seq)))]
+  (println
+    (apply max
+      (filter some?
+        (for [y (range -2000 2000)] (path-height target-area [x y]))))))
+

diff --git a/day17/part2.clj b/day17/part2.clj
new file mode 100644 (file)
index 0000000..234818f
--- /dev/null
+++ b/day17/part2.clj
@@ -0,0 +1,44 @@
+(def target-area [[169 -68] [206 -108]])
+;(def target-area [[20 -5] [30 -10]])
+(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)] [(if (pos? vx) (dec vx) 0) (dec vy)]])
+
+(defn path-builder [vel] (iterate apply-velocity [initial-pos vel]))
+
+(defn build-path [target vel]
+  (->> (path-builder vel)
+       (take-while (comp not (partial beyond-target? target) first))
+       (map first)))
+
+(defn path-height [target vel]
+  (let [path (build-path target vel)]
+    (when (within-target? target (last path))
+      (apply max (map second path)))))
+
+; 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)))
+      lowest-y     (second te)
+      valid-paths  (filter (comp some? first)
+                    (for [y (range lowest-y 2000)]
+                      [(path-height target-area [lowest-x y]) y]))
+      highest-path (reduce #(if (> (first %1) (first %2)) %1 %2) valid-paths)]
+  (println (first highest-path))
+  (println
+    (count
+      (filter (partial within-target? target-area)
+        (let [ys [(second te) (second highest-path)]]
+          (for [x (range lowest-x (inc (first te)))
+                y (range (apply min ys) (inc (apply max ys)))]
+            (last (build-path target-area [x y]))))))))
+