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Kotlin-based LeetCode algorithm problem solutions, regularly updated
443\. String Compression
Medium
Given an array of characters `chars`, compress it using the following algorithm:
Begin with an empty string `s`. For each group of **consecutive repeating characters** in `chars`:
* If the group's length is `1`, append the character to `s`.
* Otherwise, append the character followed by the group's length.
The compressed string `s` **should not be returned separately**, but instead, be stored **in the input character array `chars`**. Note that group lengths that are `10` or longer will be split into multiple characters in `chars`.
After you are done **modifying the input array,** return _the new length of the array_.
You must write an algorithm that uses only constant extra space.
**Example 1:**
**Input:** chars = ["a","a","b","b","c","c","c"]
**Output:** Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"]
**Explanation:** The groups are "aa", "bb", and "ccc". This compresses to "a2b2c3".
**Example 2:**
**Input:** chars = ["a"]
**Output:** Return 1, and the first character of the input array should be: ["a"]
**Explanation:** The only group is "a", which remains uncompressed since it's a single character.
**Example 3:**
**Input:** chars = ["a","b","b","b","b","b","b","b","b","b","b","b","b"]
**Output:** Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"].
**Explanation:** The groups are "a" and "bbbbbbbbbbbb". This compresses to "ab12".
**Constraints:**
* `1 <= chars.length <= 2000`
* `chars[i]` is a lowercase English letter, uppercase English letter, digit, or symbol.