A Constant-Factor Approximation Algorithm for the <i>k</i>-Median Problem (Extended Abstract).

Moses Charikar Sudipto Guha Éva Tardos David B. Shmoys A Constant-Factor Approximation Algorithm for the <i>k</i>-Median Problem (Extended Abstract). 1-10 1999 STOC http://doi.acm.org/10.1145/301250.301257 db/conf/stoc/stoc1999.html#CharikarGTS99