  The assignment problem takes as input two finite point sets S and T and
establishes a correspondence between points in S and points in T, such that
each point in S maps to exactly one point in T, and each point in T maps to at
least one point in S. In this paper we show that this problem has an O(n log
n)-time solution, provided that the points in S and T are restricted to lie on
a line (linear time, if S and T are presorted).
