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80 lines
2.5 KiB
Markdown
80 lines
2.5 KiB
Markdown
# [830. Positions of Large Groups](https://leetcode.com/problems/positions-of-large-groups/)
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## 题目
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In a string `s` of lowercase letters, these letters form consecutive groups of the same character.
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For example, a string like `s = "abbxxxxzyy"` has the groups `"a"`, `"bb"`, `"xxxx"`, `"z"`, and `"yy"`.
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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]`.
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A group is considered **large** if it has 3 or more characters.
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Return *the intervals of every **large** group sorted in **increasing order by start index***.
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**Example 1:**
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```
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Input: s = "abbxxxxzzy"
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Output: [[3,6]]
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Explanation: "xxxx" is the only large group with start index 3 and end index 6.
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```
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**Example 2:**
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```
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Input: s = "abc"
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Output: []
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Explanation: We have groups "a", "b", and "c", none of which are large groups.
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```
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**Example 3:**
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```
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Input: s = "abcdddeeeeaabbbcd"
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Output: [[3,5],[6,9],[12,14]]
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Explanation: The large groups are "ddd", "eeee", and "bbb".
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```
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**Example 4:**
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```
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Input: s = "aba"
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Output: []
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```
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**Constraints:**
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- `1 <= s.length <= 1000`
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- `s` contains lower-case English letters only.
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## 题目大意
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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 。
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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。
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## 解题思路
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- 简单题。利用滑动窗口的思想，先扩大窗口的右边界，找到能相同字母且能到达的最右边。记录左右边界。再将窗口的左边界移动到上一次的右边界处。以此类推，重复扩大窗口的右边界，直至扫完整个字符串。最终所有满足题意的较大分组区间都在数组中了。
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## 代码
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```go
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package leetcode
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func largeGroupPositions(S string) [][]int {
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res, end := [][]int{}, 0
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for end < len(S) {
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start, str := end, S[end]
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for end < len(S) && S[end] == str {
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end++
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}
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if end-start >= 3 {
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res = append(res, []int{start, end - 1})
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}
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}
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return res
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}
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``` |