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  2. Twelvefold way - Wikipedia

    en.wikipedia.org/wiki/Twelvefold_way

    In combinatorics, the twelvefold way is a systematic classification of 12 related enumerative problems concerning two finite sets, which include the classical problems of counting permutations, combinations, multisets, and partitions either of a set or of a number.

  3. List of NP-complete problems - Wikipedia

    en.wikipedia.org/wiki/List_of_NP-complete_problems

    The problem for graphs is NP-complete if the edge lengths are assumed integers. The problem for points on the plane is NP-complete with the discretized Euclidean metric and rectilinear metric. The problem is known to be NP-hard with the (non-discretized) Euclidean metric. [3]: ND22, ND23

  4. Enumerative combinatorics - Wikipedia

    en.wikipedia.org/wiki/Enumerative_combinatorics

    Two examples of this type of problem are counting combinations and counting permutations. More generally, given an infinite collection of finite sets S i indexed by the natural numbers , enumerative combinatorics seeks to describe a counting function which counts the number of objects in S n for each n .

  5. Stars and bars (combinatorics) - Wikipedia

    en.wikipedia.org/wiki/Stars_and_bars_(combinatorics)

    It can be used to solve a variety of counting problems, such as how many ways there are to put n indistinguishable balls into k distinguishable bins. [4] The solution to this particular problem is given by the binomial coefficient ( n + k − 1 k − 1 ) {\displaystyle {\tbinom {n+k-1}{k-1}}} , which is the number of subsets of size k − 1 ...

  6. Dunst Opening - Wikipedia

    en.wikipedia.org/wiki/Dunst_Opening

    The Dunst Opening is a chess opening in which White opens with the move: . 1. Nc3. This fairly uncommon opening may have more names than any other: it is also called the Heinrichsen Opening, Baltic Opening, Van Geet Opening, Sleipnir Opening, Kotrč's Opening, Meštrović Opening, Romanian Opening, Queen's Knight Attack, Queen's Knight Opening, Millard's Opening, Knight on the Left, and (in ...

  7. Ars Conjectandi - Wikipedia

    en.wikipedia.org/wiki/Ars_Conjectandi

    It covers most notably his theory of permutations and combinations; the standard foundations of combinatorics today and subsets of the foundational problems today known as the twelvefold way. It also discusses the motivation and applications of a sequence of numbers more closely related to number theory than probability; these Bernoulli numbers ...

  8. NP (complexity) - Wikipedia

    en.wikipedia.org/wiki/NP_(complexity)

    Euler diagram for P, NP, NP-complete, and NP-hard set of problems. Under the assumption that P ≠ NP, the existence of problems within NP but outside both P and NP-complete was established by Ladner. [1] In computational complexity theory, NP (nondeterministic polynomial time) is a complexity class used to classify decision problems.

  9. Karp's 21 NP-complete problems - Wikipedia

    en.wikipedia.org/wiki/Karp's_21_NP-complete_problems

    In computational complexity theory, Karp's 21 NP-complete problems are a set of computational problems which are NP-complete.In his 1972 paper, "Reducibility Among Combinatorial Problems", [1] Richard Karp used Stephen Cook's 1971 theorem that the boolean satisfiability problem is NP-complete [2] (also called the Cook-Levin theorem) to show that there is a polynomial time many-one reduction ...