Get on the String

You are given a string $s$, of length $n$. You have to output all the sub-sequences of $s$, with length exactly equal to $n$, in increasing order, each in a new line. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements. For ex.: $abc$ is a sub-sequence of $abdc$, while $acb$ is not. ###I