@article{Ruskey1999, 
     author = "Ruskey, Frank and Sawada, Joe", 
     doi = "10.1137/S0097539798344112", 
     issn = "0097-5397", 
     journal = "SIAM Journal on Computing", 
     keyword = "05-04,1,68r05,68r15,ams subject classifications,cat algorithm,difference covers,fixed density,generate,introduction,lyndon words,necklaces,pii,produc-,s0097539798344112,there are many reasons,to develop algorithms for", 
     link = "http://link.aip.org/link/SMJCAT/v29/i2/p671/s1\&Agg=doi http://epubs.siam.org/doi/abs/10.1137/S0097539798344112", 
     month = "jan", 
     number = "2", 
     pages = "671--684", 
     title = "An Efficient Algorithm for Generating Necklaces With Fixed Density", 
     uri = "http://link.aip.org/link/SMJCAT/v29/i2/p671/s1&Agg=doi", 
     volume = "29", 
     year = "1999", 
}

Problems: 42