830. Positions of Large Groups

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830. Positions of Large Groups

题目描述

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”.

Call a group large if it has 3 or more characters. We would like the starting and ending positions of every large group.

The final answer should be in lexicographic order.

Example 1:

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Input: "abbxxxxzzy"
Output: [[3,6]]
Explanation: "xxxx" is the single large group with starting  3 and ending positions 6.

Example 2:

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Input: "abc"
Output: []
Explanation: We have "a","b" and "c" but no large group.

Example 3:

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Input: "abcdddeeeeaabbbcd"
Output: [[3,5],[6,9],[12,14]]

Note: 1 <= S.length <= 1000

题目大意

求字符串内连续重复的字符区间。却连续重复字符数大于等于 3

解题思路

按照题目遍历字符串即可。

代码

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class Solution {
    func largeGroupPositions(_ S: String) -> [[Int]] {
        var last = S.first!
        var count = 0
        var ans = [[Int]]()
        for (i, char) in (S+"#").enumerated() {
            if last == char {
                count += 1
            }else {
                if count >= 3 {
                    ans.append([i-count, i-1])
                }
                last = char
                count = 1
            }
        }
        return ans
    }
}
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