ReformatPhoneNumber.cpp

// Source : https://leetcode.com/problems/reformat-phone-number/
// Author : Hao Chen
// Date   : 2021-05-07

/***************************************************************************************************** 
 *
 * 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.
 ******************************************************************************************************/

class Solution {
public:
    string reformatNumber(string number) {
        string result;
        for(int i=0, cnt=0; i<number.size(); i++){
            if(number[i] == ' ' or number[i] == '-') continue;
            result += number[i] ;
            cnt++;
            if (cnt % 3 == 0) result += '-';
        }
        
        int end = result.size()-1;
        if (result[end] == '-') result.erase(end, 1);
        if (result[end-1] == '-') swap(result[end-2] , result[end-1]);
        return result;
    }
};