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Problem

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: “ACGAATTCCG”. When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.

Write a function to find all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule.

Example:

Input: s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"

Output: ["AAAAACCCCC", "CCCCCAAAAA"]

Code

class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        HashSet<String> seen = new HashSet<>();
        HashSet<String> repeated = new HashSet<>();

        for(int i = 0; i < s.length() - 9; i++){
            String temp = s.substring(i, i + 10);
            if(!seen.add(temp)){
                repeated.add(temp);
            }
        }

        return new ArrayList<>(repeated);
    }
}