Fixes #9943 (#10252)

* added doctest for all_permutations.py

* added doctest for all_subsequences.py

* added doctest for all_subsequences.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* doctest added

* updated

* Update backtracking/all_subsequences.py

---------

Co-authored-by: Harsh Buddhdev <harshbuddhdev5@.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>