Initial commit

17.jl

@@ -0,0 +1,54 @@
+include("utils.jl")
+
+function parse_input(filename)
+    line = collect(non_empty_lines(filename))[1]
+    println(line)
+    map(x->parse(Int, x.match), eachmatch(r"-?[0-9]+", line))
+end
+
+function inverse_gauss(x)
+    sqrt(1/4 + 2 * x) - 1/2
+end
+
+function valid_x_velocities(left, right)
+    Int64(ceil(inverse_gauss(left))):Int64(floor(inverse_gauss(right)))
+end
+
+function hitp(left, right, bottom, top, vel)
+    pos = [0, 0]
+    mpos = [0, 0]
+    velocity = copy(vel)
+    while pos[2] > bottom
+        pos += velocity
+        mpos = max(pos, mpos)
+        velocity[1] = velocity[1] > 0 ? velocity[1] - 1 : 0
+        velocity[2] -= 1
+
+        if pos[1] >= left && pos[1] <= right && pos[2] >= bottom && pos[2] <= top
+            return true, mpos[2], vel
+        end
+    end
+    false, mpos[2], vel
+end
+
+function solution17_1()
+    left, right, bottom, top = parse_input("17.data")
+    for vx in valid_x_velocities(left, right)
+        shots = map(v->hitp(left, right, bottom, top, v), [[vx, vy] for vy in 1:10000])
+        hits = collect(Iterators.filter(x->x[1], shots))
+        println(last(sort(hits, by=x->x[2])))
+    end
+end
+
+function solution17_2()
+    left, right, bottom, top = parse_input("17.data")
+    sum = 0
+    for vx in 1:right
+        shots = map(v->hitp(left, right, bottom, top, v), [[vx, vy] for vy in bottom:1000])
+        hits = collect(map(x->x[3], Iterators.filter(x->x[1], shots)))
+        sum += length(hits)
+    end
+    sum
+end
+
+solution17_2()