Problem Narrative

A fintech company streams millions of mobile app audit logs per minute to detect suspicious behavior. To reduce bandwidth and storage costs, the client SDK performs on-device compression before upload. Because this runs on low-memory devices and must avoid GC pressure, the compression must be done in-place.

Task

You are given a list of characters chars representing a log payload. Compress it in-place using the following rule:

• Consecutive repeating characters form a group.
• Replace each group with the character followed by the group's length if the length > 1.
• The length is written as its decimal digits (e.g., 12 becomes '1','2').

Return the new length of the compressed list. The first k characters of chars must contain the compressed result, where k is the returned length. You must use O(1) extra space (excluding the input array itself).

Input / Output

• Input: chars: list[str] where each element is a single-character string
• Output: int (the length of the compressed content)

Examples

Example 1

Input: chars = ['a','a','b','b','c','c','c']

Output: 6

Explanation (step-by-step):

• 'a' repeats 2 times → write 'a','2'
• 'b' repeats 2 times → write 'b','2'
• 'c' repeats 3 times → write 'c','3' Compressed prefix becomes ['a','2','b','2','c','3'].

Example 2

Input: chars = ['a']

Output: 1

Explanation: Only one 'a', so we keep it as-is with no count.

Constraints

• 1 <= chars.length <= 2 * 10^5
• chars[i] is a lowercase English letter, uppercase English letter, digit, or symbol
• You must modify chars in-place with O(1) extra space

Notes / Clarifications

• The compressed output is guaranteed to fit within the original array length for this problem.
• Returning the length is required because the array may have leftover characters beyond the compressed prefix.