My Rosh Yeshiva, Reb Meilach Kaplan z”l of Lod Israel told me one may buy a lottery ticket provided one has another source of income, not every week so as not to be considered a gambler who is posul le-eidus rather every second or third week, only a government lottery that benefits the community like lotto that builds hospitals and schools etc’… so it will not be considered asmachta and gezel ch”v