  This paper presents an algorithm that achieves hyper-arc consistency for the
soft alldifferent constraint. To this end, we prove and exploit the equivalence
with a minimum-cost flow problem. Consistency of the constraint can be checked
in O(nm) time, and hyper-arc consistency is achieved in O(m) time, where n is
the number of variables involved and m is the sum of the cardinalities of the
domains. It improves a previous method that did not ensure hyper-arc
consistency.
