LeetCode: Compress string question

compressString.java

class Solution {
    public int compress(char[] chars) {
        var len = chars.length;
        var count = 1;
        if (len == 1){
            return count;
        }
        var mark = 0;
        var charCnt = 1;
        for (int i = 1; i < len; i++){
            if (chars[i-1] == chars[i]){
                charCnt++;
            } else {
                mark = write(chars, charCnt, mark, i);
                charCnt = 1;
            }
        }
        if (charCnt == 1){
            chars[mark++] = chars[len -1];
        } else {
            mark = write(chars, charCnt, mark, (len -1));
        }
        return mark;
    }

    private int write(char[] chars, int charCnt, int mark, int i){
        chars[mark++] = chars[i-1];
        if (charCnt > 1){
            var str = String.valueOf(charCnt);
            var slen = str.length();
            var j = 0;
            while (j < slen){
                chars[mark++] = str.charAt(j++);
            }
        }
        return mark;
    }
}

Achievement

The above code is implemented by me which beats 97% of the total solutions submitted in terms of runtime as per the Leet code console.