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Initial data commit

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Ingy döt Net 2023-07-01 11:58:00 -04:00
parent 72d218235f
commit f23f22d71c
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Task/Quickselect-algorithm/AppleScript/quickselect-algorithm-1.applescript Normal file
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on quickselect(theList, l, r, k)
script o
property lst : theList's items -- Shallow copy.
end script
repeat
-- Median-of-3 pivot selection.
set leftValue to item l of o's lst
set rightValue to item r of o's lst
set pivot to item ((l + r) div 2) of o's lst
set leftGreaterThanRight to (leftValue > rightValue)
if (leftValue > pivot) then
if (leftGreaterThanRight) then
if (rightValue > pivot) then set pivot to rightValue
else
set pivot to leftValue
end if
else if (pivot > rightValue) then
if (leftGreaterThanRight) then
set pivot to leftValue
else
set pivot to rightValue
end if
end if
-- Initialise pivot store indices and swap the already compared outer values here if necessary.
set pLeft to l - 1
set pRight to r + 1
if (leftGreaterThanRight) then
set item r of o's lst to leftValue
set item l of o's lst to rightValue
if (leftValue = pivot) then
set pRight to r
else if (rightValue = pivot) then
set pLeft to l
end if
else
if (leftValue = pivot) then set pLeft to l
if (rightValue = pivot) then set pRight to r
end if
-- Continue three-way partitioning.
set i to l + 1
set j to r - 1
repeat until (i > j)
set leftValue to item i of o's lst
repeat while (leftValue < pivot)
set i to i + 1
set leftValue to item i of o's lst
end repeat
set rightValue to item j of o's lst
repeat while (rightValue > pivot)
set j to j - 1
set rightValue to item j of o's lst
end repeat
if (j > i) then
if (leftValue = pivot) then
set pRight to pRight - 1
if (pRight > j) then
set leftValue to item pRight of o's lst
set item pRight of o's lst to pivot
end if
end if
if (rightValue = pivot) then
set pLeft to pLeft + 1
if (pLeft < i) then
set rightValue to item pLeft of o's lst
set item pLeft of o's lst to pivot
end if
end if
set item j of o's lst to leftValue
set item i of o's lst to rightValue
else if (i > j) then
exit repeat
end if
set i to i + 1
set j to j - 1
end repeat
-- Swap stored pivot(s) into a central partition.
repeat with p from l to pLeft
if (j > pLeft) then
set item p of o's lst to item j of o's lst
set item j of o's lst to pivot
set j to j - 1
else
set j to p - 1
exit repeat
end if
end repeat
repeat with p from r to pRight by -1
if (i < pRight) then
set item p of o's lst to item i of o's lst
set item i of o's lst to pivot
set i to i + 1
else
set i to p + 1
exit repeat
end if
end repeat
-- If k's in either of the outer partitions, repeat for that partition. Othewise return the item in slot k.
if (k ≥ i) then
set l to i
else if (k ≤ j) then
set r to j
else
return item k of o's lst
end if
end repeat
end quickselect
-- Task code:
set theVector to {9, 8, 7, 6, 5, 0, 1, 2, 3, 4}
set selected to {}
set vectorLength to (count theVector)
repeat with i from 1 to vectorLength
set end of selected to quickselect(theVector, 1, vectorLength, i)
end repeat
return selected