Suppose that each member of a set of agents has a preference list of a subset
of houses, possibly involving ties and each agent and house has their capacity
denoting the maximum number of correspondingly agents/houses that can be
matched to him/her/it. We want to find a matching $M$, for which there is no
other matching $M'$ such that more agents prefer $M'$ to $M$ than $M$ to $M'$.
(What it means that an agent prefers one matching to the other is explained in
the paper.) Popular matchings have been studied quite extensively, especially
in the one-to-one setting.
We give a 3/2-approximation algorithm for stable matchings that runs in
$O(m)$ time. The previously best known algorithm by McDermid has the same
approximation ratio but runs in $O(n^{3/2}m)$ time, where $n$ denotes the
number of vertices and $m$ the number of edges. Also the algorithm and the
analysis are much simpler.