Consecutive Characters

Problem Statement

The concept of the power of a string refers to the length of the longest contiguous segment (or substring) within the string that contains exactly one unique character. Given a string s, the task is to calculate its power. This involves identifying the longest substring where the same single character repeats consecutively without any interruption of a different character.

Examples

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.

Constraints

• 1 <= s.length <= 500
• s consists of only lowercase English letters.

Approach and Intuition

To solve this problem, we aim to find the maximum length of a substring which is composed entirely of the same character. The approach involves iterating through the string s while maintaining a count of consecutive characters. Here's a step-by-step breakdown:

1. Initialize two variables: max_power to store the maximum length of such substrings and current_power to count consecutive characters as you traverse the string.
2. Iterate through the string from the first character to the last.
3. Compare each character with the previous one:
   • If they are the same, increment the current_power.
   • If they are different, update max_power if current_power is greater, and reset current_power to 1 (since the new different character starts its own potential substring).
4. After the loop, there might be a case where the longest substring is at the end of the string. Therefore, compare and potentially update max_power with current_power one last time.
5. The value of max_power at the end of these steps will be the power of the string.

Below are the example walkthroughs based on the given examples:

• Example 1: "leetcode"
  • The contiguous repeats of 'e' form the longest substrings of the same character, and the length is 2.
• Example 2: "abbcccddddeeeeedcba"
  • The sequence of 'e' repeated five times consecutively forms the longest such segment with a length of 5.

These insights showcase how to tackle the problem by focusing on consecutive characters and ensure the solution adheres to the constraints that the input string length will not exceed 500 characters, and only lowercase English letters are included.

Solutions

class Solution {
    public int longestRepetition(String str) {
        int currentCount = 0;
        int maximumCount = 0;
        char lastChar = ' ';
        for (int index = 0; index < str.length(); index++) {
            char currentChar = str.charAt(index);
            if (currentChar == lastChar) {
                currentCount++;
            } else {
                currentCount = 1;
                lastChar = currentChar;
            }
            maximumCount = Math.max(maximumCount, currentCount);
        }
        return maximumCount;
    }
}