A subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements (source: wiki). Expected time complexity is linear.

What is a subsequence in a string?

A String is a subsequence of a given String, that is generated by deleting some character of a given string without changing its order. Examples: Input : abc Output : a, b, c, ab, bc, ac, abc Input : aaa Output : a, aa, aaa. Recommended: Please try your approach on {IDE} first, before moving on to the solution.

How do you define subsequence?

In mathematics, a subsequence of a given sequence is a sequence that can be derived from the given sequence by deleting some or no elements without changing the order of the remaining elements.