What does 'Positions of Large Groups' refer to?

It refers to identifying groups of consecutive characters in a string that are larger than 2 characters and returning their intervals.

How do I identify large groups in the string?

A group is considered large if it contains more than two consecutive characters of the same type. The solution requires identifying such groups and returning their start and end indices.

What is the optimal time complexity for this problem?

The optimal time complexity is O(N), where N is the length of the string, since each character is checked once.

Can the solution handle strings up to the maximum length?

Yes, the solution is designed to handle strings up to 1000 characters, maintaining an O(N) time complexity.

What is a common mistake to avoid in this problem?

A common mistake is to incorrectly count groups that are not large enough, such as groups with only 2 characters.

#830

Easy

auto_awesomeString-driven solution strategy

LeetCode 题解工作台

较大分组的位置

在一个由小写字母构成的字符串 s 中，包含由一些连续的相同字符所构成的分组。例如，在字符串 s = "abbxxxxzyy" 中，就含有 "a" , "bb" , "xxxx" , "z" 和 "yy" 这样的一些分组。分组可以用区间 [start, end] 表示，其中 start 和 end…

字符串

题目描述

在一个由小写字母构成的字符串 s 中，包含由一些连续的相同字符所构成的分组。

例如，在字符串 s = "abbxxxxzyy" 中，就含有 "a", "bb", "xxxx", "z" 和 "yy" 这样的一些分组。

分组可以用区间 [start, end] 表示，其中 start 和 end 分别表示该分组的起始和终止位置的下标。上例中的 "xxxx" 分组用区间表示为 [3,6] 。

我们称所有包含大于或等于三个连续字符的分组为 较大分组 。

找到每一个 较大分组 的区间，按起始位置下标递增顺序排序后，返回结果。

示例 1：

输入：s = "abbxxxxzzy"
输出：[[3,6]]
解释："xxxx" 是一个起始于 3 且终止于 6 的较大分组。

示例 2：

输入：s = "abc"
输出：[]
解释："a","b" 和 "c" 均不是符合要求的较大分组。

示例 3：

输入：s = "abcdddeeeeaabbbcd"
输出：[[3,5],[6,9],[12,14]]
解释：较大分组为 "ddd", "eeee" 和 "bbb"

示例 4：

输入：s = "aba"
输出：[]

提示：

1 <= s.length <= 1000
s 仅含小写英文字母

lightbulb

解题思路

方法一：双指针

我们用双指针 $i$ 和 $j$ 找到每个分组的起始位置和终止位置，然后判断分组长度是否大于等于 $3$ ，若是则将其加入结果数组。

时间复杂度 $O(n)$ ，其中 $n$ 为字符串 $s$ 的长度。

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class Solution:
    def largeGroupPositions(self, s: str) -> List[List[int]]:
        i, n = 0, len(s)
        ans = []
        while i < n:
            j = i
            while j < n and s[j] == s[i]:
                j += 1
            if j - i >= 3:
                ans.append([i, j - 1])
            i = j
        return ans

speed

复杂度分析

指标	值
时间	O(N)
空间	O(N)

psychology

面试官常问的追问

外企场景

question_mark
Candidates should demonstrate knowledge of efficient string iteration techniques.
question_mark
Look for candidates to properly handle string boundary cases, such as transitions between characters.
question_mark
Assess if candidates correctly identify the necessary conditions for a group to be considered large.

warning

常见陷阱

外企场景

error
Incorrectly including groups of size 2 as large groups.
error
Failing to handle boundary cases where groups start or end at the beginning or end of the string.
error
Overcomplicating the problem by using unnecessary data structures or multiple passes.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Consider handling uppercase letters or strings with mixed cases (though constraints specify lowercase).
arrow_right_alt
What if the string contained digits instead of letters? Can the solution still work?
arrow_right_alt
Optimize for a scenario where the string is very large (close to 1000 characters).

help

常见问题

外企场景

继续练习

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