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lostcauz · Dec 16th, 2004, 5:38 AM

In a numerical spiral such as below the question was given to determine the sum of both diagonals in a 1001 by 1001 spiral.

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73 74 75 76 77 78 79 80 81
72 43 44 45 46 47 48 49 50
71 42 21 22 23 24 25 26 51
70 41 20 7 8 9 10 27 52
69 40 19 6 1 2 11 28 53
68 39 18 5 4 3 12 29 54 
67 38 17 16 15 14 13 30 55
66 37 36 35 34 33 32 31 56
65 64 63 62 61 60 59 58 57

I'm curious what algorithm others would have chosen. Mine follows.
I noticed a pattern with the diagonal numbers
- every 4th iteration add 2

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 2 2 2 2 4 4 4 4 6 6 6 6 8 8 8 8 
1,3,5,7,9,13,17,21,25,31,37,43,49,57,65,73,81

So I set an inner loop counter at 4 and incremented a reg by 2 each time.

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 mov ecx, 1   ; first diagonal spiral number
 xor ebx, ebx  ; determines distance to next diagonal
 mov eax, ecx  ; begin accumulating sum
inner:
 add ebx, 2   ; update distance between diagonals
 mov edx, 4   ; will use distancefor 4 iterations
outer:
 add ecx, ebx  ; go to next diagonal
 cmp ecx, 1002001; is it the last one?
 ja getout   ; yes, go away
 add eax, ecx  ; no, add to sum
 dec edx     ; decrement inner loop counter
 jz inner    ; if zero- reset counter
 jmp outer    ; next number
getout:

Dec 16th, 2004, 5:38 AM	#1
lostcauz Hobbyist Programmer Join Date: Nov 2004 Location: 1691 miles East of L.A. Posts: 159 Rep Power: 5	In a numerical spiral such as below the question was given to determine the sum of both diagonals in a 1001 by 1001 spiral. (Toggle Plain Text) 73 74 75 76 77 78 79 80 81 72 43 44 45 46 47 48 49 50 71 42 21 22 23 24 25 26 51 70 41 20 7 8 9 10 27 52 69 40 19 6 1 2 11 28 53 68 39 18 5 4 3 12 29 54 67 38 17 16 15 14 13 30 55 66 37 36 35 34 33 32 31 56 65 64 63 62 61 60 59 58 57 73 74 75 76 77 78 79 80 81 72 43 44 45 46 47 48 49 50 71 42 21 22 23 24 25 26 51 70 41 20 7 8 9 10 27 52 69 40 19 6 1 2 11 28 53 68 39 18 5 4 3 12 29 54 67 38 17 16 15 14 13 30 55 66 37 36 35 34 33 32 31 56 65 64 63 62 61 60 59 58 57 I'm curious what algorithm others would have chosen. Mine follows. I noticed a pattern with the diagonal numbers - every 4th iteration add 2 (Toggle Plain Text) 2 2 2 2 4 4 4 4 6 6 6 6 8 8 8 8 1,3,5,7,9,13,17,21,25,31,37,43,49,57,65,73,81 2 2 2 2 4 4 4 4 6 6 6 6 8 8 8 8 1,3,5,7,9,13,17,21,25,31,37,43,49,57,65,73,81 So I set an inner loop counter at 4 and incremented a reg by 2 each time. (Toggle Plain Text) mov ecx, 1 ; first diagonal spiral number xor ebx, ebx ; determines distance to next diagonal mov eax, ecx ; begin accumulating sum inner: add ebx, 2 ; update distance between diagonals mov edx, 4 ; will use distancefor 4 iterations outer: add ecx, ebx ; go to next diagonal cmp ecx, 1002001; is it the last one? ja getout ; yes, go away add eax, ecx ; no, add to sum dec edx ; decrement inner loop counter jz inner ; if zero- reset counter jmp outer ; next number getout: mov ecx, 1 ; first diagonal spiral number xor ebx, ebx ; determines distance to next diagonal mov eax, ecx ; begin accumulating sum inner: add ebx, 2 ; update distance between diagonals mov edx, 4 ; will use distancefor 4 iterations outer: add ecx, ebx ; go to next diagonal cmp ecx, 1002001; is it the last one? ja getout ; yes, go away add eax, ecx ; no, add to sum dec edx ; decrement inner loop counter jz inner ; if zero- reset counter jmp outer ; next number getout: __________________ -- lostcauz Stepped in what?... Behind whose barn?... I didn't even know they had a cow!