k-d Tree Nearest Neighbor Search

NNS(q: point, n: node, p: ref point w: ref distance)

if n.left = n.right = null then {leaf case}

w’ := ||q - n.point||;

if w’ < w then

w := w’;

p := n.point;

else

if q(n.axis) < n.value then {query to left}

NNS(q, n.left, p, w);

if q(n.axis) + w > n.value then NNS(q, n.right, p, w);

else {query to right}

NNS(q, n.right, p, w);

if q(n.axis) - w < n.value then NNS(q, n.left, p, w)

NNS(q, root, p, infty)

initial call

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