Leetcode•Jul 20, 2025
Repeated DNA Sequences
Hazrat Ali
Leetcode
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"]
Solution
/**
* @param {string} s
* @return {string[]}
*/
const findRepeatedDnaSequences = s => {
const seen = new Set();
const repeated = new Set();
for (let i = 0; i + 9 < s.length; i++) {
const sequence = s.substring(i, i + 10);
if (seen.has(sequence)) {
repeated.add(sequence);
}
seen.add(sequence);
}
return Array.from(repeated);
};