[Julia] Day 24 brute-force

Project.toml

@@ -2,3 +2,6 @@ name = "AoC2023"
 uuid = "6a329b9a-879f-4671-b49f-bf1b928a466a"
 authors = ["all authors"]
 version = "0.1.0"
+
+[deps]
+NonlinearSolve = "8913a72c-1f9b-4ce2-8d82-65094dcecaec"

inputs/24_example.txt

@@ -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

solutions/24_moelf.txt

@@ -0,0 +1,2 @@
+17867
+557743507346379

src/julia/24_moelf.jl

@@ -0,0 +1,83 @@
+struct Hail
+    pos::NTuple{3,Int}
+    vel::NTuple{3,Int}
+end
+
+slopey(h) = big(h.vel[2]) / h.vel[1]
+slopez(h) = big(h.vel[3]) / h.vel[1]
+isfuture(h, x0) = sign(x0 - h.pos[1]) == sign(h.vel[1])
+
+function intersect(h1, h2)
+    x1, y1 = h1.pos
+    x2, y2 = h2.pos
+    S1, S2 = slopey(h1), slopey(h2)
+    x0 = (y2 - y1 - S2 * x2 + S1 * x1) / (S1 - S2)
+    y0 = (x0 - x1) * S1 + y1
+
+    x0, y0
+end
+
+function forecast(h, x0)
+    x, y, z = h.pos
+    Sy = slopey(h)
+    Sz = slopez(h)
+    Δy = (x0 - x) * Sy
+    Δz = (x0 - x) * Sz
+    return (x0, y + Δy, z + Δz)
+end
+
+function impl2(hails, v_extrema)
+    xlim, ylim, zlim = v_extrema
+    for xi in range(xlim...), yi in 0:100
+        v_offset = (xi, yi, 0)
+        dummy = [Hail(x.pos, x.vel .- v_offset) for x in hails]
+        h1, rest... = dummy
+        xy = intersect(h1, rest[1])
+        x0 = xy[1]
+        isinf(x0) && continue
+        if all(h -> all(intersect(h1, h) .≈ xy), rest)
+            for zi in range(zlim...)
+                v_offset = (xi, yi, zi)
+                dummy2 = [Hail(x.pos, x.vel .- v_offset) for x in hails]
+                h2, rest2... = dummy2
+                est = forecast(h2, x0)
+                if all(h -> all(forecast(h, x0) .≈ est), rest2)
+                    return sum(round.(BigInt, est))
+                end
+            end
+        end
+    end
+    error("no solution")
+end
+
+function main(path)
+    vs = Int[]
+
+    hails = map(eachline(path)) do line
+        l, r = split(line, " @ ")
+        pos = Tuple(parse.(Int, split(l, ", ")))
+        vel = Tuple(parse.(Int, split(r, ", ")))
+        append!(vs, vel)
+        Hail(pos, vel)
+    end
+
+    v_extrema = extrema.(eachrow(reshape(vs, 3, :)))
+
+    p1 = 0
+    for i in eachindex(hails), j in i+1:lastindex(hails)
+        h1 = hails[i]
+        h2 = hails[j]
+        x0, y0 = intersect(h1, h2)
+        !isfuture(h1, x0) && continue
+        !isfuture(h2, x0) && continue
+        if all(x -> 200000000000000 <= x <= 400000000000000, (x0, y0))
+            p1 += 1
+        end
+    end
+    println(p1)
+
+    println(impl2(hails, v_extrema))
+end
+
+
+(abspath(PROGRAM_FILE) == @__FILE__) && main(ARGS[1])