practice_prob: Solve incremental subsequence

Signed-off-by: Prashant Malani <p.malani@gmail.com>
csort: Implement counting sort algorithm

Signed-off-by: Prashant Malani <p.malani@gmail.com>
permute: Implementation of permutations of a string

Signed-off-by: Prashant Malani <p.malani@gmail.com>