1 files changed, 31 insertions, 0 deletions
diff --git a/day03.rb b/day03.rb
new file mode 100644
index 0000000..e8b2d86
--- /dev/null
+++ b/day03.rb
@@ -0,0 +1,31 @@
+require 'pp'
+
+d = 368078
+
+N = 20
+a = Array.new(N) { Array.new(N, 0) }
+
+x = y = N/2
+a[x][y] = 1
+
+y += 1
+
+2.step(10, 2) { |n|
+  steps = Array.new(n-1, [-1, 0]) +
+          Array.new(n,   [ 0,-1]) +
+          Array.new(n,   [ 1, 0]) +
+          Array.new(n+1, [ 0, 1])
+  steps.each { |(dx,dy)|
+    a[x][y] = a[x-1][y-1] + a[x-1][y] + a[x-1][y+1] + 
+              a[x  ][y-1] +             a[x  ][y+1] + 
+              a[x+1][y-1] + a[x+1][y] + a[x+1][y+1]
+    if a[x][y] > d
+      p a[x][y]
+      exit
+    end
+    x += dx
+    y += dy
+  }
+}
+
+a.each { |l| p l }