LeetCode 1694. Reformat Phone Number

Description

https://leetcode.com/problems/reformat-phone-number/

You are given a phone number as a string numbernumber 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.

Explanation

We can record the numbers first, then keep grouping 3 numbers in a group until less than 4 numbers. If 4 numbers left, divide to 2 groups, otherwise group to 1 group.

Python Solution

class Solution:
    def reformatNumber(self, number: str) -> str:
        number_list = []
        
        for c in number:
            if c.isdigit():
                number_list.append(c)
            
        
        start = 0
        
        groups = defaultdict(list)
        
        while len(number_list) > 4:  
            size = len(groups)
            for i in range(3):            
                groups[size].append(number_list.pop(0))
            
        if len(number_list) == 4:
            size = len(groups)            
            for i in range(2):            
                groups[size].append(number_list.pop(0))            

            size = len(groups)            
                
            for i in range(2):            
                groups[size].append(number_list.pop(0))   
                
        else:
            size = len(groups)            
            
            for i in range(len(number_list)):            
                groups[size].append(number_list.pop(0))              

        
        result = []
        for key, value in groups.items():
            result.append("".join(value))
                                            
        
        return "-".join(result)
            
            
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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