Python backtracking method to achieve array array output instance analysis

This article illustrates an example of python backtracking method to achieve array array output. Share with you for your reference. Specific analysis is as follows:

Explanation of full arrangement: take m (m Or less n) elements from n different elements, arrange them in a certain order, it is called an arrangement of taking m elements from n different elements. All permutations when m is equal to n are called all permutations.

from sys import stdout
#code from //www.jb51.net/
def perm(li, start, end):
  if(start == end):
    for elem in li:
      stdout.write(elem)
    print ''
  else:
    for i in range(start, end):
      li[start], li[i] = li[i], li[start]
      perm(li, start+1, end)
      li[i], li[start] = li[start], li[i]
if __name__ == '__main__':
  li = ['a','b','c','d']
  perm(li, 0, len(li))

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