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Grokking the Coding Interview Patterns in Python

Repeated DNA Sequences

Explore how to detect repeated 10-letter sequences in DNA strings using the sliding window approach. This lesson helps you understand substring identification and efficient string manipulation to solve pattern recognition problems common in coding interviews.

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Statement

A DNA sequence consists of a series of nucleotides, each represented by one of the characters 'A', 'C', 'G', or 'T'.

Given a string s representing a DNA sequence, find and return all 1010-letter-long substrings that appear more than once within s. The result may be returned in any order.

Constraints:

  • 1≤1 \leq s.length ≤105\leq 10^5

  • s[i] is one of 'A', 'C', 'G', or 'T'

Examples

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Understand the problem

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Repeated DNA Sequences

1.

Given the input s = "TTTTTTTTT", what is the output of finding all 1010-letter-long substrings that appear more than once?

A.

["TTTTTTTTT"]

B.

["TTTTTTTTTT"]

C.

[]

D.

["TTTTTTTTT", "TTTTTTTTTT"]

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in the following coding playground.

Python
usercode > solution.py
def findRepeatedDnaSequences(s):
    
    # Replace this placeholder return statement with your code 
    return list("O")
Repeated DNA Sequences