示例 1：
输入：chars = ["a","a","b","b","c","c","c"]输出：返回 6 ，输入数组的前 6 个字符应该是：["a","2","b","2","c","3"]解释："aa" 被 "a2" 替代。"bb" 被 "b2" 替代。"ccc" 被 "c3" 替代。
来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/string-compression著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

    public int compress(char[] chars) {        StringBuilder builder = new StringBuilder();        int n = chars.length;        char temp = chars[0];        int cnt = 0;        for (int i = 0; i < n; i++) {            if (temp == chars[i]) {                cnt++;            } else {                builder.append(temp);                if (cnt != 1) {                    builder.append(cnt);                }                temp = chars[i];                cnt = 1;            }        }                builder.append(temp);        if (cnt != 1) {            builder.append(cnt);        }
        String s = builder.toString();        int ans = s.length();        for (int i = 0 ; i < ans; i++) {            chars[i] = s.charAt(i);        }        return ans;    }

    public int compress(char[] chars) {        int n = chars.length;        int i = 0;         int j = 0;        while (i < n) {            int idx = i;            while (idx < n && chars[idx] == chars[i]) {                idx++;            }            int cnt = idx - i;            chars[j++] = chars[i];            if (cnt > 1) {                int start = j, end = start;                while (cnt != 0) {                    chars[end++] = (char) ((cnt % 10) + '0');                    cnt /= 10;                }                reverse(chars, start, end - 1);                j = end;            }            i = idx;        }
        return j;    }
    public void reverse(char[] cs, int start, int end) {        while (start < end) {            char t = cs[start];            cs[start] = cs[end];            cs[end] = t;            start++; end--;        }    }