rmo's definition?
Anyway, here's an approach which works on the indices.
Please note that I haven't tested it thoroughly for boundary problems.
I just consider the rising diagonals as extra columns. Top & bottom
indices will be reduplicated, but can be removed with nub.
eg for LHA = 5, we get this index array:
0 8 (8)
1 7 9
2 6 10
3 5 11 ..
4 (4) 12 (12)
It actually works on the transpose first.
cv =: 3 : 0
:
n =. x
difs =. (,:~|.) +:@i. n <.l =. #y
start=. i.n<.l
nstep=. (0 >. l-n) >.@% n-1
y{~ l-.~ ~.l<.,|:+/\start,nstep$difs
)
3 4 5 cv each/ '';'paypa';1 2 3 4;'paypalishiring'
++-----+-------+--------------+
||paapy|1 2 4 3|pahnaplsiigyir|
++-----+-------+--------------+
||payap|1 2 3 4|pinalsigyahrpi|
++-----+-------+--------------+
||paypa|1 2 3 4|phasiyirpligan|
++-----+-------+--------------+
Any use?
Mike
On 27/09/2016 13:02, 'Jon Hough' via Programming wrote:
This is a programming challenge from here:
https://leetcode.com/problems/zigzag-conversion/
The challenge is to convert a string into a "zig zag" formation with the given
number of rows.
e.g. (from the link)
PAYPALISHIRING is transformed into PAHNAPLSIIGYIR (the link explains clearly
this transformation)
This is my solution, which works.
NB. Convert text into a zigzag text.
NB. x: number of row (positive integer)
NB. y: string text
convert =: 4 : 0
rows =. x
text =. y
len =. # y
if. 0 = len do. ''
elseif. 1 = len do. text
elseif. 1 = rows do. text
elseif. 1 do.
k=. 0
l=. 0
res =. ''
NB. loop through the rows
while. (k < rows) *. k < len do.
res =. res, k{text
NB. how much to increment. first and last rows are special
NB. cases, inner rows switch the increment.
nextMax =. (2 * rows) - 2
rm1 =. rows - 1
l1 =. ((+:@:(rm1&-))`(nextMax&[)@.((rmo&=)+.(0&=))) k
l2 =. ((+:)`(nextMax&[)@.((rm1&=)+.(0&=)))k
NB. first incremented value
nextIndex =. k + l1
NB. flag indicates which increment to use.
flag =. 1
while. nextIndex < len do.
res =. res, nextIndex{text
flag =. (flag = 0)
if. flag do. nextIndex =. nextIndex + l1
else. nextIndex =. nextIndex + l2
end.
end.
k =. k + 1 NB. increment the row
end.
res
end.
)
3 convert 'PAYPALISHIRING'
It's an interesting challenge and I'm sure there is a much nicer way to do this
in J...
Regards,
Jon
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