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Kleitman–Wang algorithms : ウィキペディア英語版 | Kleitman–Wang algorithms The Kleitman–Wang algorithms are two different algorithms in graph theory solving the digraph realization problem, i.e. the question if there exists for a finite list of nonnegative integer pairs a simple directed graph such that its degree sequence is exactly this list. For a positive answer the list of integer pairs is called ''digraphic''. Both algorithms construct a special solution if one exists or prove that one cannot find a positive answer. These constructions are based on recursive algorithms. Kleitman and Wang gave these algorithms in 1973. ==Kleitman–Wang algorithm (arbitrary choice of pairs)== The algorithm is based on the following theorem. Let be a finite list of nonnegative integers that is in nonincreasing lexicographical order and let be a pair of nonnegative integers with . List is digraphic if and only if the finite list has nonnegative integer pairs and is digraphic. Note that the pair is arbitrarily with the exception of pairs . If the given list digraphic then the theorem will be applied at most times setting in each further step . This process ends when the whole list consists of pairs. In each step of the algorithm one constructs the arcs of a digraph with vertices , i.e. if it is possible to reduce the list to , then we add arcs . When the list cannot be reduced to a list of nonnegative integer pairs in any step of this approach, the theorem proves that the list from the beginning is not digraphic.
抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Kleitman–Wang algorithms」の詳細全文を読む
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