1694. Reformat Phone Number

1694. Reformat Phone Number (Easy)

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".

Example 4:

Input: number = "12"
Output: "12"

Example 5:

Input: number = "--17-5 229 35-39475 "
Output: "175-229-353-94-75"

 

Constraints:

• 2 <= number.length <= 100
• number consists of digits and the characters '-' and ' '.
• There are at least two digits in number.

Related Topics:
String

Solution 1.

// OJ: https://leetcode.com/problems/reformat-phone-number/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    string reformatNumber(string s) {
        int j = 0;
        for (int i = 0; i < s.size(); ++i) {
            if (isdigit(s[i])) s[j++] = s[i];
        }
        s.resize(j);
        string ans;
        for (int i = 0, r = s.size(); i < s.size(); ) {
            for (int d = r == 2 || r == 4 ? 2 : 3; d > 0; --d, --r) {
                ans += s[i++];
            }
            if (r) ans += '-';
        }
        return ans;
    }
};