Detect Repeated Patterns in a String Sequence

Question

The candidate is asked to implement a solution to detect repeated patterns in a given string sequence.

Codemia · Accepted Answer

To detect repeated patterns in a string, I will use a combination of string slicing and a hash set to track seen patterns. The idea is to iterate through the string and check for substrings of varying lengths, storing each substring in the hash set. If we encounter a substring that already exists in the set, we have found a repeated pattern.

1. Initialize an empty hash set to store substrings.
2. Loop through the string with two nested loops: the outer loop for the starting index and the inner loop for the length of the substring.
3. For each substring, check if it exists in the hash set.
4. If it does, return the substring as a repeated pattern; if not, add it to the set.
5. If no repeated patterns are found by the end of the loops, return an indication that there are none.

The time complexity of this approach is O(n^2) in the worst case, where n is the length of the string, due to the nested loops. The space complexity is O(n) for storing the substrings in the hash set.

```python
def detect_repeated_pattern(s):
    seen = set()
    n = len(s)
    for i in range(n):
        for length in range(1, n - i + 1):
            substring = s[i:i + length]
            if substring in seen:
                return substring
            seen.add(substring)
    return None
```
This code defines a function that detects the first repeated substring in the input string.

It is important to consider edge cases such as an empty string, which should return None, and strings without any repeated patterns, which should also return None. Additionally, handling strings with special characters should not affect the algorithm's ability to detect patterns.

Detect Repeated Patterns in a String Sequence

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