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