LeetCode in Kotlin

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”.t

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.

Solution

class Solution {
    fun reformatNumber(number: String): String {
        val sb = StringBuilder()
        for (c in number.toCharArray()) {
            if (Character.isDigit(c)) {
                sb.append(c)
            }
        }
        val cleaned = sb.toString()
        sb.setLength(0)
        var i = 0
        while (i < cleaned.length) {
            i += if (i + 4 == cleaned.length) {
                sb.append(cleaned, i, i + 2)
                sb.append("-")
                sb.append(cleaned.substring(i + 2))
                break
            } else if (i + 3 <= cleaned.length) {
                sb.append(cleaned, i, i + 3)
                sb.append("-")
                3
            } else {
                sb.append(cleaned.substring(i))
                break
            }
        }
        if (sb[sb.length - 1] == '-') {
            sb.setLength(sb.length - 1)
        }
        return sb.toString()
    }
}

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