Day 17: Clojure (Part 1)

Author: Siphalor

17-clojure/input/input

@@ -0,0 +1 @@
+target area: x=195..238, y=-93..-67

17-clojure/input/simple

@@ -0,0 +1 @@
+target area: x=20..30, y=-10..-5

17-clojure/main.clj

@@ -0,0 +1,56 @@
+(if (not (== (count *command-line-args*) 2))
+  (do
+    (println "incorrect number of arguments")
+    (System/exit 1)))
+
+(defn traceShot
+  [tx1 ty1 tx2 ty2 x y vx vy]
+  (do
+    (cond
+      (or (> x tx2) (< y ty2)) false 
+      (and (>= x tx1) (<= y ty1)) true
+      :else (recur
+              tx1 ty1 tx2 ty2
+              (+ x vx)
+              (+ y vy)
+              (cond
+                (< vx 0) (+ vx 1)
+                (> vx 0) (- vx 1)
+                :else 0
+              )
+              (- vy 1)))))
+
+(def ^:const DEBUG false)
+(def ^:const UNCHANGED_CNT 50)
+
+(def highest (atom [ -1 0 ]))
+(def fileContent (slurp (last *command-line-args*)))
+(let [ [ _ g1 g2 g3 g4 ]
+      (map read-string (re-find #"target area: x=(-?\d+)\.\.(-?\d+), y=(-?\d+)\.\.(-?\d+)\s*" fileContent))
+      ]
+  (let [ unchanged (atom UNCHANGED_CNT)
+         tx1 (min g1 g2)
+         tx2 (max g1 g2)
+         ty1 (max g3 g4)
+         ty2 (min g3 g4)
+         vy (atom ty1) ]
+    (while (> @unchanged 0)
+      (if DEBUG (println "vy:" @vy))
+      (let [ vx (atom 0) ]
+        (swap! vx (vector 0))
+        (while (<= @vx tx1)
+          (if (traceShot tx1 ty1 tx2 ty2 0 0 @vx @vy)
+            (do
+              (if DEBUG (println "found vx:" @vx "vy:" @vy))
+              (swap! highest (constantly [ @vx @vy ]))
+              (swap! unchanged (constantly UNCHANGED_CNT))))
+          (swap! vx inc))
+      (swap! vy inc))
+
+      (if (> @vy 0) (swap! unchanged dec))
+      (if DEBUG (println @unchanged "unchanged left")))
+    )
+  )
+
+(println "best pair:" @highest)
+(println "largest height:" (* (/ (second @highest) 2) (+ (second @highest) 1)))