Day 17 part 2 solutions

Author: creideiki

17-2.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python
+
+import re
+
+line = open('17.input').read().strip()
+
+target_format = re.compile("^target area: x=(?P<x1>[0-9\-]+)..(?P<x2>[0-9\-]+), y=(?P<y1>[0-9\-]+)..(?P<y2>[0-9\-]+)$")
+
+m = target_format.match(line)
+
+x_min = int(m['x1'])
+x_max = int(m['x2'])
+y_min = int(m['y1'])
+y_max = int(m['y2'])
+
+# Possible x velocities:
+# Maximum: hits x_max on the first time step
+x_vel_max = x_max
+
+# Minimum: decellerates to x_vel=0 before x_min
+# Distance travelled = (1 + x_vel) * x_vel / 2
+#                 start ^    ^ end    ^ x_steps
+x_vel_min = 0
+for x_vel in range(x_min):
+    if (1 + x_vel) * x_vel / 2 >= x_min:
+        x_vel_min = x_vel
+        break
+
+# Possible y velocities:
+# Maximum: lobs up, hits y=0 at launch velocity, hits y=y_min at next step
+y_vel_max = abs(y_min) - 1
+
+# Minimum: directly to y_min at first step
+y_vel_min = y_min
+
+
+def simulate(x_vel, y_vel, x_min, x_max, y_min, y_max):
+    x = 0
+    y = 0
+    while x <= x_max and y >= y_min:
+        if x >= x_min and x <= x_max and \
+           y >= y_min and y <= y_max:
+            return True
+
+        x += x_vel
+        y += y_vel
+        if x_vel > 0:
+            x_vel -= 1
+        y_vel -= 1
+
+    return False
+
+
+count = 0
+for x_vel in range(x_vel_min, x_vel_max + 1):
+    for y_vel in range(y_vel_min, y_vel_max + 1):
+        if simulate(x_vel, y_vel, x_min, x_max, y_min, y_max):
+            count += 1
+
+print(count)

17-2.rb

@@ -0,0 +1,60 @@
+#!/usr/bin/env ruby
+
+input = File.read('17.input').strip
+
+target_format = /^target area: x=(?<x1>[[:digit:]\-]+)..(?<x2>[[:digit:]\-]+), y=(?<y1>[[:digit:]\-]+)..(?<y2>[[:digit:]\-]+)$/
+
+m = target_format.match(input)
+
+x_min = m['x1'].to_i
+x_max = m['x2'].to_i
+y_min = m['y1'].to_i
+y_max = m['y2'].to_i
+
+# Possible x velocities:
+# Maximum: hits x_max on the first time step
+x_vel_max = x_max
+
+# Minimum: decellerates to x_vel=0 before x_min
+# Distance travelled = (1 + x_vel) * x_vel / 2
+#                 start ^    ^ end    ^ x_steps
+x_vel_min = 0
+x_min.times do |x_vel|
+  if (1 + x_vel) * x_vel / 2 >= x_min
+    x_vel_min = x_vel
+    break
+  end
+end
+
+# Possible y velocities:
+# Maximum: lobs up, hits y=0 at launch velocity, hits y=y_min at next step
+y_vel_max = y_min.abs - 1
+
+# Minimum: directly to y_min at first step
+y_vel_min = y_min
+
+def simulate(x_vel, y_vel, x_min, x_max, y_min, y_max)
+  x = 0
+  y = 0
+  while x <= x_max and y >= y_min
+    return true if
+      x >= x_min and x <= x_max and
+      y >= y_min and y <= y_max
+
+    x += x_vel
+    y += y_vel
+    x_vel -= 1 if x_vel.positive?
+    y_vel -= 1
+  end
+  false
+end
+
+count = 0
+x_vel_min.upto(x_vel_max) do |x_vel|
+  y_vel_min.upto(y_vel_max) do |y_vel|
+    if simulate(x_vel, y_vel, x_min, x_max, y_min, y_max)
+      count += 1
+    end
+  end
+end
+print count, "\n"