In combinatorial mathematics, a Langford pairing, also called a Langford sequence, is a permutation of the sequence of 2n numbers 1, 1, 2, 2, ..., n,n in which the two ones are one unit apart, the two twos are two units apart, and more generally the two copies of each number k are k units apart.

For example:

Langford pairing for n = 3 is given by the sequence 2,3,1,2,1,3.

  • What is a good method to solve this in haskell or C
  • Can you suggest an algorithm to solve it (Do not want to use brute force)?

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How could we define the mathematical rules to put @Rafe's code in haskell

c algorithm math haskell combinatorics
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