The Kirkpatrick–Seidel algorithm, proposed by its authors as a potential "ultimate planar convex hull algorithm", is an algorithm for computing the convex hull of a set of points in the plane, with O ( n log h ) {\displaystyle {\mathcal {O}}(n\log h)} time complexity, where n {\displaystyle n} is the number of input points and h {\displaystyle h} is the number of points (non dominated or maximal points, as called in some texts) in the hull. Thus, the algorithm is output-sensitive: its running time depends on both the input size and the output size. Another output-sensitive algorithm, the gift wrapping algorithm, was known much earlier, but the Kirkpatrick–Seidel algorithm has an asymptotic running time that is significantly smaller and that always improves on the O ( n log n ) {\displaystyle {\mathcal {O}}(n\log n)} bounds of non-output-sensitive algorithms. The Kirkpatrick–Seidel algorithm is named after its inventors, David G. Kirkpatrick and Raimund Seidel.
Although the algorithm is asymptotically optimal, it is not very practical for moderate-sized problems.