For a Jordan curve C in the plane nowhere tangent to the x axis, let x1, x2,..., xn be the abscissas of the intersection points of C with the x axis, listed in the order the points occur on C. We call x1, x2,..., xn a Jordan sequence. In this paper we describe an O(n)-time algorithm for recognizing and sorting Jordan sequences. The problem of sorting such sequences arises in computational geometry and computational geography. Our algorithm is based on a reduction of the recognition and sorting problem to a list-splitting problem. To solve the list-splitting problem we use level-linked search trees.
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