Leetcode – Consecutive Characters Solution

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One problem that particularly stands out for its simplicity yet its ability to test your grasp on string manipulation is the “Consecutive Characters” problem. The problem falls under the categories of string and array manipulation.

In this elaborate guide, we will walk through:

  1. Problem Statement
  2. Initial Thoughts & Brute-force Approach
  3. Optimal Approach
  4. Python Implementations
  5. Test Cases & Edge Cases
  6. Time and Space Complexity Analysis
  7. Conclusion

1. Problem Statement

Given a string s, the power of the string is the maximum length of a non-empty substring that contains only one unique character. Return the power of the string.

Example 1:

Input: s = "leetcode"
Output: 2
Explanation: The substring “ee” is of length 2 with the character ‘e’ only.

Example 2:

Input: s = "abbcccddddeeeeedcba"
Output: 5
Explanation: The substring “eeeee” is of length 5 with the character ‘e’ only.

2. Initial Thoughts & Brute-force Approach

A straightforward way to solve this problem would be to iterate over the string while maintaining a counter and a temporary character variable. For each character, we would compare it with the next one. If they match, we increment the counter; otherwise, we reset the counter.

3. Optimal Approach

The brute-force solution is not bad, but we can streamline the process. We can solve it in a single pass by maintaining two variables: one for the current streak of consecutive characters and another for the maximum streak seen so far. This will allow us to find the maximum length of a substring with consecutive characters in O(n) time complexity, where nn is the length of the string.

4. Python Implementations

Brute-force Implementation

def maxPower(s):
    max_power = 1
    current_power = 1
    for i in range(len(s) - 1):
        if s[i] == s[i + 1]:
            current_power += 1
            max_power = max(max_power, current_power)
            current_power = 1
    return max(max_power, current_power)

Optimal Implementation

In this case, the optimal implementation is essentially the same as the brute-force one since we can solve the problem in a single pass.

5. Test Cases & Edge Cases

It’s important to validate your code with various test cases:

# Test 1
assert maxPower("leetcode") == 2
# Test 2
assert maxPower("abbcccddddeeeeedcba") == 5
# Test 3 (Edge case)
assert maxPower("a") == 1
# Test 4 (Edge case)
assert maxPower("aa") == 2

6. Time and Space Complexity Analysis

Time Complexity

The time complexity for both the brute-force and optimal solution is O(n), where n is the length of the string. This is because we iterate over the string once.

Space Complexity

The space complexity is O(1) for both implementations as we only use a constant amount of extra memory for storing variables.

7. Conclusion

The “Consecutive Characters” problem is a straightforward yet instructive problem that provides a good opportunity to understand and practice the basics of string manipulation in Python. While the problem can be solved using a brute-force approach, it also allows for an optimal solution that only requires a single pass through the string, yielding O(n)O(n) time complexity.

This guide has aimed to provide you with a clear understanding of how to approach the problem, offering Python code implementations for both brute-force and optimal solutions. We also discussed the importance of testing your code rigorously against different test and edge cases and concluded with an analysis of time and space complexity.

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