Introduction

In this blog post, we will explore how to solve the LeetCode problem "830" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

In a string s of lowercase letters, these letters form consecutive groups of the same character. For example, a string like s = "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z", and "yy". A group is identified by an interval [start, end], where start and end denote the start and end indices (inclusive) of the group. In the above example, "xxxx" has the interval [3,6]. A group is considered large if it has 3 or more characters. Return the intervals of every large group sorted in increasing order by start index. Example 1: Input: s = "abbxxxxzzy" Output: [[3,6]] Explanation: "xxxx" is the only large group with start index 3 and end index 6. Example 2: Input: s = "abc" Output: [] Explanation: We have groups "a", "b", and "c", none of which are large groups. Example 3: Input: s = "abcdddeeeeaabbbcd" Output: [[3,5],[6,9],[12,14]] Explanation: The large groups are "ddd", "eeee", and "bbb". Constraints: 1 <= s.length <= 1000 s contains lowercase English letters only.

Explanation

Here's a solution to the problem of identifying large groups in a string, focusing on efficiency and clarity.

• Iterate and Group: The solution iterates through the string, identifying consecutive groups of the same character.
• Check Size: For each identified group, the size is checked. If the size is 3 or more, the start and end indices of the group are added to the result.

• Maintain Indices: We maintain the start index of each potential group and compare each character to the previous one to detect the group boundaries.

• Runtime Complexity: O(n), where n is the length of the string.

• Storage Complexity: O(k), where k is the number of large groups. In the worst-case scenario where the input string consists only of repetitions, k could approach n, so O(n).

Code

    def largeGroupPositions(s: str) -> list[list[int]]:
    """
    Finds the intervals of every large group (3 or more characters) in a string.

    Args:
        s: The input string of lowercase letters.

    Returns:
        A list of intervals [start, end] representing the large groups,
        sorted in increasing order by start index.
    """

    result = []
    start = 0
    for i in range(len(s)):
        if i == len(s) - 1 or s[i] != s[i + 1]:
            if i - start + 1 >= 3:
                result.append([start, i])
            start = i + 1
    return result