cp's OEIS Frontend

A220102 Permutation of natural numbers arising from applying the walk of square spiral (e.g. A214526) to the data of double square spiral (defined in A220098).

%I A220102 #8 Dec 05 2012 12:20:34
%S A220102 1,2,4,6,8,3,5,7,9,11,13,15,17,19,21,23,25,10,12,14,16,18,20,22,24,26,
%T A220102 28,30,32,34,36,38,40,42,44,46,48,27,29,31,33,35,37,39,41,43,45,47,49,
%U A220102 51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,50,52,54,56
%N A220102 Permutation of natural numbers arising from applying the walk of square spiral (e.g. A214526) to the data of double square spiral (defined in A220098).
%o A220102 (C)
%o A220102 #include <stdio.h>
%o A220102 #define SIZE 20
%o A220102 int grid[SIZE][SIZE];
%o A220102 int direction[] = {0, -1,  1, 0, 0, 1, -1, 0};
%o A220102 main() {
%o A220102   int i, j, x1, y1, x2, y2, stepSize;
%o A220102   int direction1pos=0, direction2pos=4, val;
%o A220102   x1 = y1 = x2 = y2 = SIZE/2;
%o A220102   for (val=grid[y1][x1]=1, stepSize=0; ; ++stepSize) {
%o A220102     if (x1<1 || x1>=SIZE-1 || x2<1 || x2>=SIZE-1) break;
%o A220102     if (y1<1 || y1>=SIZE-1 || y2<1 || y2>=SIZE-1) break;
%o A220102     for (i=stepSize|1; i; ++val,--i) {
%o A220102       x1 += direction[direction1pos  ];
%o A220102       y1 += direction[direction1pos+1];
%o A220102       x2 += direction[direction2pos  ];
%o A220102       y2 += direction[direction2pos+1];
%o A220102       grid[y1][x1] = val*2;
%o A220102       grid[y2][x2] = val*2+1;
%o A220102     }
%o A220102     direction1pos = (direction1pos+2) & 7;
%o A220102     direction2pos = (direction2pos+2) & 7;
%o A220102   }
%o A220102   direction1pos=0;
%o A220102   x1 = y1 = SIZE/2;
%o A220102   for (stepSize=2; ; ++stepSize) {
%o A220102     for (i=stepSize/2; i; --i) {
%o A220102       if (grid[y1][x1]==0) return;
%o A220102       printf("%d, ",grid[y1][x1]);
%o A220102       x1 += direction[direction1pos  ];
%o A220102       y1 += direction[direction1pos+1];
%o A220102     }
%o A220102     direction1pos = (direction1pos+2) & 7;
%o A220102   }
%o A220102 }
%Y A220102 Cf. A214526, A220098, A217010, A217011, A217012, A217013, A217014, A217015.
%K A220102 nonn
%O A220102 1,2
%A A220102 _Alex Ratushnyak_, Dec 04 2012