Referring to the source code of scipy.misc.comb, the update routine of the result is: val = 1 for j in xrange(min(k, N-k)): val = (val*(N-j))//(j+1) return val whereas the update routine you suggested is: ntok = 1 ktok = 1 for t in xrange(1, min(k, n – k) + 1): ntok *= n ktok *= … Read more
First, I’ll show you a recursive version. typedef std::vector<int> Vi; typedef std::vector<Vi> Vvi; // recursive algorithm to to produce cart. prod. // At any given moment, “me” points to some Vi in the middle of the // input data set. // for int i in *me: // add i to current result // recurse on … Read more
(Because it was unclear in the original version of the question whether you meant to remove a subsequence or an unordered list, I’ve updated my answer to address both cases.) 1. Removing a sub-sequence in order We get a sequence of values, e.g. [1,5,1,3,4,2,3,2,1,3,1,2], and a sub-sequence of values to be removed from the first … Read more
Use itertools.permutations: >>> import itertools >>> stuff = [1, 2, 3] >>> for L in range(0, len(stuff)+1): for subset in itertools.permutations(stuff, L): print(subset) … () (1,) (2,) (3,) (1, 2) (1, 3) (2, 1) (2, 3) (3, 1) …. Help on itertools.permutations: permutations(iterable[, r]) –> permutations object Return successive r-length permutations of elements in the … Read more
Know your Array#product: a = [[‘1′,’2’],[‘a’,’b’],[‘x’,’y’]] a.first.product(*a[1..-1]).map(&:join)
The complexity is O(C(n,k)) which is O(n choose k). This ends up being equivalent to O(min(n^k, n^(n-k))).
This is a well-studied problem of generating all k-subsets, or k-combinations, which can be easily done without recursion. The idea is to have array of size k keeping sequence of indices of elements from the input array (which are numbers from 0 to n – 1) in increasing order. (Subset then can be created by … Read more
The ndgrid function almost gives the answer, but has one caveat: n output variables must be explicitly defined to call it. Since n is arbitrary, the best way is to use a comma-separated list (generated from a cell array with ncells) to serve as output. The resulting n matrices are then concatenated into the desired … Read more