Repeated DNA Sequences

Problem

The DNA sequence is composed of a series of nucleotides abbreviated as 'A', 'C', 'G', and 'T'.

For example, "ACGAATTCCG" is a DNA sequence.

When studying DNA, it is useful to identify repeated sequences within the DNA.

Given a string s that represents a DNA sequence, return all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule. You may return the answer in any order.

Example 1:

• Input: s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"
• Output: ["AAAAACCCCC","CCCCCAAAAA"]

Example 2:

• Input: s = "AAAAAAAAAAAAA"
• Output: ["AAAAAAAAAA"]

Constraints:

• 1 <= s.length <= 105
• s[i] is either 'A', 'C', 'G', or 'T'.

Solution

Use hashset and 4-based integer.