day 17

17/17.py

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+import math
+import re
+
+with open("input") as file:
+	target = file.read().removesuffix("\n")
+	minX, maxX, minY, maxY = [int(v) for v in re.search(r"x=(.+)\.\.(.+), y=(.+)\.\.(.+)", target).groups()]
+
+# minimize the set of velocities to check via bounds
+# lower x bound cant be lower than a
+# where a(a+1)/2 = minX (little gauss)
+# because posX loses 1 every step and posX must at least reach minX
+# isolating a gives -0.5 + sqrt(0.25 + 2 * minX)
+# ceiling is enough because if minX gets a bit higher then a cannot reach it anymore
+xBounds = math.ceil(-0.5 + math.sqrt(0.25 + 2 * minX)), maxX
+
+# yPos is symmetric on the way back down and starts with 0
+yBounds = minY, -minY
+
+xRange = range(xBounds[0], xBounds[1] + 1)
+yRange = range(yBounds[0], yBounds[1] + 1)
+
+validCount = 0
+allMaxYReached = []
+
+# simulate all possible velocities
+for vx, vy in [(x, y) for x in xRange for y in yRange]:
+	posX, posY = 0, 0
+	maxYReached = 0
+	while posX <= maxX and posY >= minY:
+		if posX >= minX and posY <= maxY:
+			# target hit
+			validCount += 1
+			allMaxYReached.append(maxYReached)
+			break
+		posX += vx
+		posY += vy
+		vx -= 1 if vx > 0 else 0
+		vy -= 1
+		maxYReached = max(posY, maxYReached)
+
+print(max(allMaxYReached))
+print(validCount)

17/input

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+target area: x=201..230, y=-99..-65

17/testInput

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