LeetCode 1694. Reformat Phone Number

You are given a phone number as a string number. number consists of digits, spaces ' ', and/or dashes '-'.

You would like to reformat the phone number in a certain manner. Firstly, remove all spaces and dashes. Then, group the digits from left to right into blocks of length 3 until there are 4 or fewer digits. The final digits are then grouped as follows:

• 2 digits: A single block of length 2.

• 3 digits: A single block of length 3.

• 4 digits: Two blocks of length 2 each.

The blocks are then joined by dashes. Notice that the reformatting process should never produce any blocks of length 1 and produce at most two blocks of length 2.

Return the phone number after formatting.

Example 1:

Input: number = "1-23-45 6"

Output: "123-456"

Explanation:

The digits are "123456". 

Step 1: There are more than 4 digits, so group the next 3 digits. The 1st block is "123". 

Step 2: There are 3 digits remaining, so put them in a single block of length 3. The 2nd block is "456". Joining the blocks gives "123-456".

Example 2:

Input: number = "123 4-567"

Output: "123-45-67"

Explanation: The digits are "1234567". 

Step 1: There are more than 4 digits, so group the next 3 digits. The 1st block is "123". 

Step 2: There are 4 digits left, so split them into two blocks of length 2. The blocks are "45" and "67". Joining the blocks gives "123-45-67".

Example 3:

Input: number = "123 4-5678"

Output: "123-456-78"

Explanation: The digits are "12345678". 

Step 1: The 1st block is "123". 

Step 2: The 2nd block is "456". 

Step 3: There are 2 digits left, so put them in a single block of length 2.

The 3rd block is "78". Joining the blocks gives "123-456-78".

Constraints:

• 2 <= number.length <= 100

• number consists of digits and the characters '-' and ' '.

• There are at least two digits in number.

先将数据收集不要其他的字符，其次就是依次去遍历字符串，每次要前3个数字，直到最后生效的数字<=4的时候，去判断，如果等于4个，截取2个字符+"-"+最后2个字符，如果其他的话，直接加上即可，

下面是代码，我一开始用index去遍历，结果老是 出错，也不知道是哪里出问题了。。。

Runtime: 6 ms, faster than 27.83% of Java online submissions for Reformat Phone Number.

Memory Usage: 42.6 MB, less than 15.09% of Java online submissions for Reformat Phone Number.