# 5 Best Ways to Find Length of Substring with Consecutive Common Characters in Python

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π‘ Problem Formulation: This article delves into the challenge of computing the length of the longest substring wherein all characters are consecutive and identical within a given string. For instance, given “aabbbcdd”, the desired output is “3” due to the substring “bbb”.

## Method 1: Iterative Comparison

This method uses a simple loop to iterate through the string, comparing each character with the next one, to find the longest length of consecutive common characters. It initializes a counter and updates the maximum length found at each step.

Here’s an example:

```def longest_consecutive_substring(s):
max_length = 1
current_length = 1
for i in range(1, len(s)):
if s[i] == s[i-1]:
current_length += 1
max_length = max(max_length, current_length)
else:
current_length = 1
return max_length

print(longest_consecutive_substring("aabbbcdd"))  # Example usage```

The output of this code snippet is `3`.

This method is straightforward and easy to understand. It walks through the string once, which gives it an O(n) time complexity, making it efficient for even very long strings.

## Method 2: Groupby from itertools

Utilizes the `groupby` function from Python’s `itertools` module to group consecutive characters. This method abstracts the iteration process and automatically handles grouping of identical adjacent characters.

Here’s an example:

```from itertools import groupby

def longest_consecutive_substring(s):
return max(len(list(group)) for key, group in groupby(s))

print(longest_consecutive_substring("aabbbcdd"))  # Example usage```

The output of this code snippet is `3`.

This method is concise and leverages the power of itertools for processing iterables. The resulting code is easier to read and write but may be a bit more difficult for beginners to understand initially.

## Method 3: Using Regular Expressions

This approach employs Python’s `re` module to find all consecutive characters using regular expressions. It highlights the ability to use pattern matching to solve string manipulation problems.

Here’s an example:

```import re

def longest_consecutive_substring(s):
matches = re.finditer(r'(.)\1*', s)
return max(len(match.group(0)) for match in matches)

print(longest_consecutive_substring("aabbbcdd"))  # Example usage```

The output of this code snippet is `3`.

This method uses the power of regular expressions (regex), which is particularly useful for pattern matching. While powerful, regex can be less performant than some direct iteration methods and has a steeper learning curve.

## Method 4: Functional Approach with max and map

The functional programming approach uses built-in functions `max` and `map` to achieve the same result. It represents a more declarative style of writing the same logic.

Here’s an example:

```def longest_consecutive_substring(s):
return max(map(len, ''.join(' ' if s[i] != s[i-1] else s[i] for i in range(1, len(s), 1)).split()))

print(longest_consecutive_substring("aabbbcdd"))  # Example usage```

The output of this code snippet is `3`.

This functional style is succinct and leverages Python’s expressive capabilities. However, it may be less intuitive and less readable for developers not familiar with functional programming.

## Bonus One-Liner Method 5: Using Recursion

A recursive function is another intriguing way to solve this problem, especially for enthusiasts of recursion. It replicates the iterative logic in a recursive manner.

Here’s an example:

```def longest_consecutive_substring(s, idx=0, max_len=1, curr_len=1):
if idx == len(s) - 1:
return max(max_len, curr_len)
if s[idx] == s[idx + 1]:
return longest_consecutive_substring(s, idx + 1, max_len, curr_len + 1)
else:
return longest_consecutive_substring(s, idx + 1, max(max_len, curr_len), 1)

print(longest_consecutive_substring("aabbbcdd"))  # Example usage```

The output of this code snippet is `3`.

Recursion is a powerful concept, but it’s not often the most optimal for this type of problem due to potential stack overflow on very long strings and typically has more overhead than iterative solutions.

## Summary/Discussion

• Method 1: Iterative Comparison. Simple and efficient. O(n) complexity. Easy to understand but verbose.
• Method 2: Groupby from itertools. Abstracts away explicit looping, which can make the code cleaner. May be less intuitive for those unfamiliar with itertools.
• Method 3: Using Regular Expressions. Very powerful for pattern matching. May have performance issues for very large strings and is harder to learn.
• Method 4: Functional Approach. Concise and expressive. Requires an understanding of Python’s functional programming features.
• Bonus Method 5: Using Recursion. Conceptually interesting. Not the most optimal for this problem and potentially dangerous for large inputs.