LeetCode 1694: Reformat Phone Number Solution

Master LeetCode problem 1694 (Reformat Phone Number), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1694. Reformat Phone Number

Easy

String

Problem Explanation

Explanation:

Remove all spaces and dashes from the input phone number.
Group the remaining digits into blocks of length 3 until there are 4 or fewer digits.
Handle the remaining digits based on the number of digits left (2, 3, or 4).

Time Complexity: O(N) where N is the length of the input phone number string. Space Complexity: O(N) for the output phone number string.

Solution Code

class Solution {
    public String reformatNumber(String number) {
        StringBuilder sb = new StringBuilder();
        for (char c : number.toCharArray()) {
            if (Character.isDigit(c)) {
                sb.append(c);
            }
        }
        
        StringBuilder result = new StringBuilder();
        int len = sb.length();
        for (int i = 0; i < len; i += 3) {
            if (len - i == 4) {
                result.append(sb.substring(i, i + 2)).append("-").append(sb.substring(i + 2, i + 4));
                break;
            } else if (len - i <= 3) {
                result.append(sb.substring(i));
                break;
            } else {
                result.append(sb.substring(i, i + 3)).append("-");
            }
        }
        
        return result.toString();
    }
}

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