Convex hull: Difference between revisions
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=={{header|jq}}==
{{trans|Wren}}
{{works with|jq}}
'''Works with gojq, the Go implementation of jq'''
<lang jq># ccw returns true if the three points make a counter-clockwise turn
def ccw(a; b; c):
a as [$ax, $ay]
| b as [$bx, $by]
| c as [$cx, $cy]
| (($bx - $ax) * ($cy - $ay)) > (($by - $ay) * ($cx - $ax)) ;
def convexHull:
if . == [] then []
else sort as $pts
# lower hull:
| reduce $pts[] as $pt ([];
until (length < 2 or ccw(.[-2]; .[-1]; $pt); .[:-1] )
| . + [$pt] )
# upper hull
| (length + 1) as $t
| reduce range($pts|length-2; -1; -1) as $i (.;
$pts[$i] as $pt
| until (length < $t or ccw(.[-2]; .[-1]; $pt); .[:-1] )
| . + [$pt])
| .[:-1]
end ;</lang>
'''The task'''
<lang jq>def pts: [
[16, 3], [12, 17], [ 0, 6], [-4, -6], [16, 6],
[16, -7], [16, -3], [17, -4], [ 5, 19], [19, -8],
[ 3, 16], [12, 13], [ 3, -4], [17, 5], [-3, 15],
[-3, -9], [ 0, 11], [-9, -3], [-4, -2], [12, 10]
];
"Convex Hull: \(pts|convexHull)"</lang>
{{out}}
<pre>
Convex Hull: [[-9,-3],[-3,-9],[19,-8],[17,5],[12,17],[5,19],[-3,15]]
</pre>
=={{header|Julia}}==
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