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  2. Closure (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Closure_(mathematics)

    In mathematics, a subset of a given set is closed under an operation of the larger set if performing that operation on members of the subset always produces a member of that subset. For example, the natural numbers are closed under addition, but not under subtraction: 1 − 2 is not a natural number, although both 1 and 2 are.

  3. Set cover problem - Wikipedia

    en.wikipedia.org/wiki/Set_cover_problem

    A fractional set cover is an assignment of a fraction (a number in [0,1]) to each set in , such that for each element x in the universe, the sum of fractions of sets that contain x is at least 1. The goal is to find a fractional set cover in which the sum of fractions is as small as possible. Note that a (usual) set cover is equivalent to a ...

  4. Subset sum problem - Wikipedia

    en.wikipedia.org/wiki/Subset_sum_problem

    Given a solution to the SubsetSumPositive instance, adding the −T yields a solution to the SubsetSumZero instance. Conversely, given a solution to the SubsetSumZero instance, it must contain the − T (since all integers in S are positive), so to get a sum of zero, it must also contain a subset of S with a sum of + T , which is a solution of ...

  5. LeetCode - Wikipedia

    en.wikipedia.org/wiki/LeetCode

    LeetCode LLC, doing business as LeetCode, is an online platform for coding interview preparation. The platform provides coding and algorithmic problems intended for users to practice coding . [ 1 ] LeetCode has gained popularity among job seekers in the software industry and coding enthusiasts as a resource for technical interviews and coding ...

  6. Covering problems - Wikipedia

    en.wikipedia.org/wiki/Covering_problems

    There is a set O of m objects, and a conflict-graph G O on O. A subset Q of O is called conflict-free if it is an independent set in G O, that is, no two objects in Q are connected by an edge in G O. A rainbow set is a conflict-free set in the special case in which G O is made of disjoint cliques, where each clique represents a color.

  7. Maximum coverage problem - Wikipedia

    en.wikipedia.org/wiki/Maximum_coverage_problem

    Second, compare the solution gained by the first step to the best solution which uses a small number of sets. Third, return the best out of all examined solutions. This algorithm achieves an approximation ratio of 11 / e − o ( 1 ) {\displaystyle 1-1/e-o(1)} .

  8. Smallest-circle problem - Wikipedia

    en.wikipedia.org/wiki/Smallest-circle_problem

    The solution of the subproblem is either the solution of the unconstrained problem or it is used to determine the half-plane where the unconstrained solution center is located. The n 16 {\textstyle {\frac {n}{16}}} points to be discarded are found as follows: The points P i are arranged into pairs which defines n 2 {\textstyle {\frac {n}{2 ...

  9. Club set - Wikipedia

    en.wikipedia.org/wiki/Club_set

    If a set is both closed and unbounded, then it is a club set. Closed proper classes are also of interest (every proper class of ordinals is unbounded in the class of all ordinals). For example, the set of all countable limit ordinals is a club set with respect to the first uncountable ordinal ; but it is not a club set with respect to any ...