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  2. Lehmer code - Wikipedia

    en.wikipedia.org/wiki/Lehmer_code

    The usual way to prove that there are n! different permutations of n objects is to observe that the first object can be chosen in n different ways, the next object in n − 1 different ways (because choosing the same number as the first is forbidden), the next in n − 2 different ways (because there are now 2 forbidden values), and so forth.

  3. Cycles and fixed points - Wikipedia

    en.wikipedia.org/wiki/Cycles_and_fixed_points

    (3.a) We may choose one of the f(k − 1, j − 1) permutations with k − 1 elements and j − 1 fixed points and add element k as a new fixed point. (3.b) We may choose one of the f(k − 1, j) permutations with k − 1 elements and j fixed points and insert element k in an existing cycle of length > 1 in front of one of the (k − 1) − j ...

  4. Permutation codes - Wikipedia

    en.wikipedia.org/wiki/Permutation_Codes

    A main problem in permutation codes is to determine the value of (,), where (,) is defined to be the maximum number of codewords in a permutation code of length and minimum distance . There has been little progress made for 4 ≤ d ≤ n − 1 {\displaystyle 4\leq d\leq n-1} , except for small lengths.

  5. Birthday problem - Wikipedia

    en.wikipedia.org/wiki/Birthday_problem

    With M = 365 days in a year, the average number of people required to find a pair with the same birthday is n = 1 + Q(M) ≈ 24.61659, somewhat more than 23, the number required for a 50% chance. In the best case, two people will suffice; at worst, the maximum possible number of M + 1 = 366 people is needed; but on average, only 25 people are ...

  6. Steinhaus–Johnson–Trotter algorithm - Wikipedia

    en.wikipedia.org/wiki/Steinhaus–Johnson...

    The ! permutations of the numbers from 1 to may be placed in one-to-one correspondence with the ! numbers from 0 to ! by pairing each permutation with the sequence of numbers that count the number of positions in the permutation that are to the right of value and that contain a value less than (that is, the number of inversions for which is the ...

  7. Programming by permutation - Wikipedia

    en.wikipedia.org/wiki/Programming_by_permutation

    Programming by permutation, sometimes called "programming by accident" or "shotgunning", is an approach to software development wherein a programming problem is solved by iteratively making small changes (permutations) and testing each change to see if it behaves as desired. This approach sometimes seems attractive when the programmer does not ...

  8. Inversion (discrete mathematics) - Wikipedia

    en.wikipedia.org/wiki/Inversion_(discrete...

    The inversions of this permutation using element-based notation are: (3, 1), (3, 2), (5, 1), (5, 2), and (5,4). In computer science and discrete mathematics , an inversion in a sequence is a pair of elements that are out of their natural order .

  9. Permutation - Wikipedia

    en.wikipedia.org/wiki/Permutation

    An exceedance of a permutation σ 1 σ 2...σ n is an index j such that σ j > j. If the inequality is not strict (that is, σ j ≥ j), then j is called a weak exceedance. The number of n-permutations with k exceedances coincides with the number of n-permutations with k descents. [46]