Given an array of characters, compress itin-place.

The length after compression must always be smaller than or equal to the original array.

Every element of the array should be acharacter(not int) of length 1.

After you are donemodifying the input arrayin-place, return the new length of the array.

Follow up:
Could you solve it using only O(1) extra space?

Example 1:

Input:

["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:

"aa" is replaced by "a2". "bb" is replaced by "b2". "ccc" is replaced by "c3".

Example 2:

Input:

["a"]


Output:

Return 1, and the first 1 characters of the input array should be: ["a"]


Explanation:

Nothing is replaced.

Example 3:

Input:

["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:

Since the character "a" does not repeat, it is not compressed. "bbbbbbbbbbbb" is replaced by "b12".
Notice each digit has it's own entry in the array.

Note:

1. All characters have an ASCII value in [35, 126] .
2. 1 < = len(chars) < = 1000 .

class Solution {
    public int compress(char[] chars) {
        if (chars == null) return 0;
        if (chars.length < 2) return chars.length;
        StringBuilder sb = new StringBuilder();
        char prev = chars[0];
        int count = 1;

        for (int i = 1; i < chars.length; i++){
            if (chars[i] == prev){
                count++;
            }
            else{
                if (count == 1){
                    sb.append(prev);
                }
                else{
                    sb.append(prev);
                    sb.append(count);
                }

                prev = chars[i];
                count = 1;
            }
        }

        if (count == 1){
            sb.append(prev);
        }
        else{
            sb.append(prev);
            sb.append(count);
        }

        for (int i = 0; i < sb.length(); i++){
            chars[i] = sb.charAt(i);
        }
        return sb.length();
    }
}