June 2018 Update

Task/Spiral-matrix/Octave/spiral-matrix.octave

@@ -1,27 +1,21 @@
-function rs = runsum(v)
-  for i = 1:numel(v)
-    rs(i) = sum(v(1:i));
+function a = spiral(n)
+  a = ones(n*n, 1);
+  u = -(i = n) * (v = ones(n, 1));
+  for k = n-1:-1:1
+    j = 1:k;
+    a(j+i) = u(j) = -u(j);
+    a(j+(i+k)) = v(j) = -v(j);
+    i += 2*k;
   endfor
+  a(cumsum(a)) = 1:n*n;
+  a = reshape(a, n, n)'-1;
 endfunction
 
-function g = grade(v)
-  for i = 1:numel(v)
-    g(v(i)+1) = i-1;
-  endfor
-endfunction
+>> spiral(5)
+ans =
 
-function spiral = make_spiral(spirald)
-  series = ones(1,spirald^2);
-  l = spirald-1; p = spirald+1;
-  s = 1;
-  while(l>0)
-    series(p:p+l-1) *= spirald*s;
-    series(p+l:p+l*2-1) *= -s;
-    p += l*2;
-    l--; s *= -1;
-  endwhile
-  series(1) = 0;
-  spiral = reshape(grade(runsum(series)), spirald, spirald)';
-endfunction
-
-make_spiral(5)
+    0    1    2    3    4
+   15   16   17   18    5
+   14   23   24   19    6
+   13   22   21   20    7
+   12   11   10    9    8