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".

Approach

Java

public class ReformateString {
    public static void main(String[] args) {

        String number = "1-23-45 6";

        System.out.println(reformatNumber(number));
    }

    static String reformatNumber(String number) {
        String res = "";
        String s = "";
        for (int i = 0; i < number.length(); i++) {
            if (number.charAt(i) >= '0' && number.charAt(i) <= '9') {
                s += number.charAt(i);
            }
        }
        int i = 0;
        while (i < s.length()) {

            if (s.length() - i == 2) {
                res += s.charAt(i);
                res += s.charAt(i + 1);

                i += 2;
            } else if (s.length() - i == 4) {
                res += s.charAt(i);
                res += s.charAt(i + 1);
                res += "-";
                res += s.charAt(i + 2);
                res += s.charAt(i + 3);
                i += 4;
            } else if (s.length() - i >= 3 && s.length() - i != 4) {
                res += s.charAt(i);
                res += s.charAt(i + 1);
                res += s.charAt(i + 2);

                i += 3;
                if (i != s.length())
                    res += "-";
            }
        }
        return res;
    }

}

C++

#include <bits/stdc++.h>
using namespace std;

string reformatNumber(string number)
{
    string res = "";
    string s = "";
    for (int i = 0; i < number.size(); i++)
    {
        if (number[i] >= '0' && number[i] <= '9')
        {
            s += number[i];
        }
    }
    int i = 0;
    while (i < s.size())
    {

        if (s.size() - i == 2)
        {
            res += s[i];
            res += s[i + 1];

            i += 2;
        }
        else if (s.size() - i == 4)
        {
            res += s[i];
            res += s[i + 1];
            res += "-";
            res += s[i + 2];
            res += s[i + 3];
            i += 4;
        }
        else if (s.size() - i >= 3 && s.size() - i != 4)
        {
            res += s[i];
            res += s[i + 1];
            res += s[i + 2];

            i += 3;
            if (i != s.size())
                res += "-";
        }
    }
    return res;
}

int main()
{
    string number = "1-23-45 6";

    cout << reformatNumber(number) << "\n";

    return 0;
}