Add 2023/24 py

erikw · web-flow · commit c43a1b78d192 · 2025-05-20T19:12:38.000Z
diff --git a/.vscode/settings.json b/.vscode/settings.json
@@ -37,6 +37,7 @@
         "pdir",
         "ppos",
         "pprev",
+        "rint",
         "starte",
         "Vandermonde"
     ],
diff --git a/2015/24/part2.rb b/2015/24/part2.rb
@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-# Props to https://www.reddit.com/r/adventofcode/comments/3y1s7f/comment/cy9sqq2/?utm_source=share&utm_medium=web2x&context=3
+# Props to https://www.reddit.com/r/adventofcode/comments/3y1s7f/comment/cy9sqq2/
 def min_quantum_packing(packages, groups)
   group_size = packages.sum / groups
   (1..packages.length).each do |len|
diff --git a/2019/16/part2.rb b/2019/16/part2.rb
@@ -8,7 +8,7 @@
 BASE_PATTERN = [0, 1, 0, -1]
 OFFSET_LEN = 7
 
-# h/t https://www.reddit.com/r/adventofcode/comments/ebf5cy/comment/fb4awi4/?utm_source=share&utm_medium=web2x&context=3
+# h/t https://www.reddit.com/r/adventofcode/comments/ebf5cy/comment/fb4awi4/
 # The key insights are
 # * we can skip computing values before the offset
 # * The offset is so large, that to calculate each digit in a phase is just the sum in that unitriangular matrix.
diff --git a/2019/19/part2.rb b/2019/19/part2.rb
@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-# h/t https://www.reddit.com/r/adventofcode/comments/ecogl3/comment/fbdmn5n/?utm_source=share&utm_medium=web2x&context=3
+# h/t https://www.reddit.com/r/adventofcode/comments/ecogl3/comment/fbdmn5n/
 # Algorithm:
 # * Fit the SHIP_DIM * SHIP_DIM square by moving it diagonally down.
 # x
diff --git a/2020/13/part2.rb b/2020/13/part2.rb
@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-# h/t https://www.reddit.com/r/adventofcode/comments/kc4njx/comment/gfnbwzc/?utm_source=share&utm_medium=web2x&context=3
+# h/t https://www.reddit.com/r/adventofcode/comments/kc4njx/comment/gfnbwzc/
 
 def ext_gcd(a, b, values)
   d = a
diff --git a/2020/23/part1_array.rb b/2020/23/part1_array.rb
@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-# h/t https://www.reddit.com/r/adventofcode/comments/kimluc/comment/ggrzza7/?utm_source=share&utm_medium=web2x&context=3
+# h/t https://www.reddit.com/r/adventofcode/comments/kimluc/comment/ggrzza7/
 # The array cups has index being the cup label and the value is the clock-wise next neighbour.
 
 require 'set'
diff --git a/2021/08/part2.rb b/2021/08/part2.rb
@@ -14,7 +14,7 @@
   '9' => 'abcdfg'       # Len = 6
 }
 
-# h/t https://www.reddit.com/r/adventofcode/comments/rbj87a/comment/hnpad75/?utm_source=share&utm_medium=web2x&context=3
+# h/t https://www.reddit.com/r/adventofcode/comments/rbj87a/comment/hnpad75/
 
 count_map = DIGIT_MAP.map(&:last).join.chars.group_by(&:itself).map { |k, v| [k, v.length] }.to_h
 countpattern2digit = DIGIT_MAP.map do |digit, pattern|
diff --git a/2021/19/part1.rb b/2021/19/part1.rb
@@ -58,7 +58,7 @@
 # end
 # end
 
-# h/t https://www.reddit.com/r/adventofcode/comments/rjpf7f/comment/hp58zmu/?utm_source=share&utm_medium=web2x&context=3
+# h/t https://www.reddit.com/r/adventofcode/comments/rjpf7f/comment/hp58zmu/
 def orient(orient_idx, x, y, z)
   case orient_idx
   when 0
diff --git a/2023/01/part2_replacement.py b/2023/01/part2_replacement.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 import fileinput
 
-# h/t https://www.reddit.com/r/adventofcode/comments/1883ibu/comment/kbielt0/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
+# h/t https://www.reddit.com/r/adventofcode/comments/1883ibu/comment/kbielt0/
 TEXT_DIGITS = {
     "one": "one1one",
     "two": "two2two",
diff --git a/2023/05/part2.py b/2023/05/part2.py
@@ -112,7 +112,7 @@ def read_seeds_maps():
     return (seeds, maps)
 
 
-# h/t https://www.reddit.com/r/adventofcode/comments/18b4b0r/comment/kc291gz/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
+# h/t https://www.reddit.com/r/adventofcode/comments/18b4b0r/comment/kc291gz/
 def main():
     seed_ranges, maps = read_seeds_maps()
     ranges = [(r[0], r[0] + r[1]) for r in seed_ranges]
diff --git a/2023/10/part2.py b/2023/10/part2.py
@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# h/t https://www.reddit.com/r/adventofcode/comments/18evyu9/comment/kcqmhwk/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
+# h/t https://www.reddit.com/r/adventofcode/comments/18evyu9/comment/kcqmhwk/
 import fileinput
 
 PIPE_NORTH_SOUTH = "|"
diff --git a/2023/20/part2.py b/2023/20/part2.py
@@ -54,7 +54,7 @@ def read_module_configuration():
 
 def find_min_presses(mod_conf):
     """
-    # h/t https://www.reddit.com/r/adventofcode/comments/18mmfxb/comment/ke5a5fc/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
+    # h/t https://www.reddit.com/r/adventofcode/comments/18mmfxb/comment/ke5a5fc/
     # With manual analysis of output from mermaid.py, it is concluded that for my input:
     # * rx is connected as: [&lr, &nl, &vr, &gt] -> &jq -> rx
     # * further it can be seen that those earlier 4 conjunctions all go to a different sub graph, namely the 4 subgraphs branching from module broadcaster.
diff --git a/2023/21/part2.py b/2023/21/part2.py
@@ -71,7 +71,7 @@ def expand_map(map, pos_start, max_steps):
 def main():
     map, pos_start = read_map()
 
-    # h/t https://www.reddit.com/r/adventofcode/comments/18nevo3/comment/keao6r4/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
+    # h/t https://www.reddit.com/r/adventofcode/comments/18nevo3/comment/keao6r4/
     # As STEPS = 202300 * len(map) + 65
     # or: 26501365 = 202300 * 131 + 65
     n = STEPS // len(map) # 202300
diff --git a/2023/24/README.md b/2023/24/README.md
@@ -0,0 +1,12 @@
+# Advent of Code - 2023 Day 24
+Here are my solutions to this puzzle.
+
+* Problem instructions: [adventofcode.com/2023/day/24](https://adventofcode.com/2023/day/24)
+* Input: [adventofcode.com/2023/day/24/input](https://adventofcode.com/2023/day/24/input)
+
+Fetch input by exporting `$AOC_SESSION` in your shell and then:
+```bash
+curl -OJLsb session=$AOC_SESSION adventofcode.com/2023/day/24/input
+```
+
+or run `fetch_input.sh` in this directory.
diff --git a/2023/24/fetch_input.sh b/2023/24/fetch_input.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env sh
+# Make sure $AOC_SESSION is exported before running this script.
+
+curl --remote-name --remote-header-name --silent --fail -A 'https://erikw.me/contact' --cookie "session=$AOC_SESSION" "https://adventofcode.com/2023/day/24/input"
+test "$?" -eq 0 && echo "Fetched input" && exit 0 || echo "Failed to fetch input" && exit 1
diff --git a/2023/24/input1.0 b/2023/24/input1.0
@@ -0,0 +1,5 @@
+19, 13, 30 @ -2,  1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @  1, -5, -3
diff --git a/2023/24/instructions.url b/2023/24/instructions.url
@@ -0,0 +1,2 @@
+[InternetShortcut]
+URL = https://adventofcode.com/2023/day/24
diff --git a/2023/24/output1.0 b/2023/24/output1.0
diff --git a/2023/24/output2.0 b/2023/24/output2.0
@@ -0,0 +1 @@
+47
diff --git a/2023/24/part1.py b/2023/24/part1.py
@@ -0,0 +1,159 @@
+#!/usr/bin/env python3
+import fileinput
+from pprint import pprint
+import re
+import itertools
+
+import numpy as np
+from termcolor import colored
+
+# XY_MIN = 7
+# XY_MAX = 27
+
+XY_MIN = 200000000000000
+XY_MAX = 400000000000000
+
+"""
+We are given a list of linear trajectories in two dimensions on x and y axis, given x_0 and y_0 for t=0, and the slope for each axis.
+E.g.
+Hailstone A: 19, 13, 30 @ -2, 1, -2
+Hailstone B: 18, 19, 22 @ -1, -1, -2
+
+Each hailstone can be written as a function of the time:
+H(t) =
+{
+    x(t) = k_x * t + x_0
+    y(t) = k_y * t + y_0
+}
+=
+|x(t)| = |k_x| * t + |x_0|
+|y(t)|   |k_y|       |y_0|
+
+
+e.g.
+H_a(t) =
+{
+    x_a(t) = -2t + 19
+    y_a(t) = t + 13
+}
+=
+|x_a(t)| = |-2| * t + |19|
+|y_a(t)|   |1|        |13|
+
+H_b(t) =
+{
+    x_b(t) = -t + 18
+    y_b(t) = -t + 19
+}
+=
+|x_b(t)| = |-1| * t + |18|
+|y_b(t)|   |-1|       |19|
+
+It's not about solving a system of equations for variable t i.e. the hailstones actually necessarily collide.
+Instead it's to see if their trajectories intersect at two possible different times t_a and t_b.
+Thus, we can see at which (x,y) both trajectories meet by setting up a system of 4 linear equations if 4 variables (x, y, t_a, t_b)
+
+H_a(t_a) = H_a(t_b)
+<=>
+x = k_xa * t_a + x_0a
+y = k_ya * t_a + y_0a
+x = k_xb * t_b + x_0b
+y = k_yb * t_b + y_0b
+<=> (parametric form)
+x - k_xa * t_a = x_0a
+y - k_ya * t_a = y_0a
+x - k_xb * t_b = x_0b
+y - k_yb * t_b = y_0b
+<=> (verbose, add missing variables)
+1 * x + 0 * y - k_xa * t_a + 0 * t_b = x_0a
+0 * x + 1 * y - k_ya * t_a + 0 * t_b = y_0a
+1 * x + 0 * y + 0 * t_a - k_xb * t_b = x_0b
+0 * x + 1 * y + 0 * t_a - k_yb * t_b = y_0b
+
+Solving this system of linear equations gives us the desired (x,y) for which the trajectories intersect, at two likely distinct times t_a and t_b.
+numpy.linalg.solve(A, b) solves A*x=b where: A - coefficient matrix, x - vector of unknowns , b - constants vector:
+
+    |1    0  -k_xa    0   |
+A = |0    1  -k_ya    0   |
+    |1    0    0    -k_xb |
+    |0    1    0    -k_yb |
+
+    [ x |
+x = | y |
+    |t_A|
+    |t_B]
+
+    |x_0a|
+b = |y0_a|
+    |x0_b|
+    |y0_b|
+"""
+
+SPLIT_PATTERN = re.compile(r", | @ ")
+
+def read_trajectories():
+    trajectories = []
+    for line in fileinput.input():
+        x0, y0, z0, kx, ky, kz = [int(d) for d in re.split(SPLIT_PATTERN, line)]
+        trajectories.append(((x0, y0, z0), (kx, ky, kz)))
+    return trajectories
+
+
+def print_status(tr1, tr2, i1, i2, vars):
+    name1 = chr(ord('A') + i1)
+    name2 = chr(ord('A') + i2)
+    print(f"Hailstone {name1}: {tr1[0]} @ {tr1[1]}")
+    print(f"Hailstone {name2}: {tr2[0]} @ {tr2[1]}")
+    if name1 == "A" and name2 == "E":
+        pass
+    match vars:
+        case None:
+            print("Hailstones' paths are parallel; they never intersect.")
+        case (x, y, t1, t2) if t1 < 0 and t2 < 0:
+            print("Hailstones' paths crossed in the past for both hailstones.")
+        case (x, y, t1, _) if t1 < 0:
+            print(f"Hailstones' paths crossed in the past for hailstone {name1}.")
+        case (x, y, _, t2) if t2 < 0:
+            print(f"Hailstones' paths crossed in the past for hailstone {name2}.")
+        case (x, y, _, _) if XY_MIN <= x <= XY_MAX and XY_MIN <= y <= XY_MAX:
+            print(f"Hailstones' paths will cross {colored("inside", attrs=["bold"])} the test area (at x={x:.5g}, y={y:.5g}).")
+        case (x, y, _, _):
+            print(f"Hailstones' paths will cross outside the test area (at x={x:.5g}, y={y:.5g}).")
+        case _:
+            print("Should not happen!")
+
+
+def trajectory_intersection(t1, t2):
+    A = np.array((
+         (1, 0, -t1[1][0], 0),
+         (0, 1, -t1[1][1], 0),
+         (1, 0, 0, -t2[1][0]),
+         (0, 1, 0, -t2[1][1]),
+         ))
+    b = np.array((t1[0][0], t1[0][1], t2[0][0], t2[0][1]))
+    try:
+        x = np.linalg.solve(A, b)
+    except np.linalg.LinAlgError:
+         return None
+    else:
+        return [v.item() for v in x] # [x, y, t_a, t_b]
+
+
+def main():
+    trajectories = read_trajectories()
+    # pprint(trajectories)
+
+    inside = 0
+    for (i1, tr1), (i2, tr2) in itertools.combinations(enumerate(trajectories), 2):
+        vars = trajectory_intersection(tr1, tr2)
+        # print_status(tr1, tr2, i1, i2, vars)
+        if vars:
+            x, y, t1, t2 = vars
+            if (XY_MIN <= x <= XY_MAX and
+                XY_MIN <= y <= XY_MAX and
+                t1 >= 0 and
+                t2 >= 0):
+                inside += 1
+    print(inside)
+if __name__ == '__main__':
+	main()
diff --git a/2023/24/part2.py b/2023/24/part2.py
diff --git a/bin/solve_day.sh b/bin/solve_day.sh

Original file line number	Diff line number	Diff line change
`@@ -14,7 +14,7 @@`
`14`	`14`	`'9' => 'abcdfg' # Len = 6`
`15`	`15`	`}`
`16`	`16`
`17`		`-# h/t https://www.reddit.com/r/adventofcode/comments/rbj87a/comment/hnpad75/?utm_source=share&utm_medium=web2x&context=3`
	`17`	`+# h/t https://www.reddit.com/r/adventofcode/comments/rbj87a/comment/hnpad75/`
`18`	`18`
`19`	`19`	`count_map = DIGIT_MAP.map(&:last).join.chars.group_by(&:itself).map { \|k, v\| [k, v.length] }.to_h`
`20`	`20`	`countpattern2digit = DIGIT_MAP.map do \|digit, pattern\|`