Repeated DNA Sequences LeetCode Solution | Easy Approach

Repeated DNA Sequences 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'.

Repeated DNA Sequences Solutions

✅Time: O(10n) = O(n)
✅Space:  O(10n) = O(n)

C++

 class Solution {
 public:
  vector<string> findRepeatedDnaSequences(string s) {
    unordered_set<string> ans;
    unordered_set<string_view> seen;
    const string_view sv(s);

    for (int i = 0; i + 10 <= s.length(); ++i) {
      if (seen.count(sv.substr(i, 10)))
        ans.insert(s.substr(i, 10));
      seen.insert(sv.substr(i, 10));
    }

    return {begin(ans), end(ans)};
  }
};

Java

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

    for (int i = 0; i + 10 <= s.length(); ++i) {
      final String seq = s.substring(i, i + 10);
      if (seen.contains(seq))
        ans.add(seq);
      seen.add(seq);
    }

    return new ArrayList<>(ans);
  }
}

Python

 class Solution:
  def findRepeatedDnaSequences(self, s: str) -> List[str]:
    ans = set()
    seen = set()

    for i in range(len(s) - 9):
      seq = s[i:i + 10]
      if seq in seen:
        ans.add(seq)
      seen.add(seq)

    return list(ans)

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