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License Key Formatting-LeetCode#482

482. License Key Formatting

You are given a license key represented as a string S which consists only alphanumeric character and dashes. The string is separated into N+1 groups by N dashes.

Given a number K, we would want to reformat the strings such that each group contains exactly K characters, except for the first group which could be shorter than K, but still must contain at least one character. Furthermore, there must be a dash inserted between two groups and all lowercase letters should be converted to uppercase.

Given a non-empty string S and a number K, format the string according to the rules described above.

Example 1:

Input: S = "5F3Z-2e-9-w", K = 4

Output: "5F3Z-2E9W"

Explanation: The string S has been split into two parts, each part has 4 characters.
Note that the two extra dashes are not needed and can be removed.

Example 2:

Input: S = "2-5g-3-J", K = 2

Output: "2-5G-3J"

Explanation: The string S has been split into three parts, each part has 2 characters except the first part as it could be shorter as mentioned above.


  1. The length of string S will not exceed 12,000, and K is a positive integer.
  2. String S consists only of alphanumerical characters (a-z and/or A-Z and/or 0-9) and dashes(-).
  3. String S is non-empty.

思路:将获得一个表示为字符串S的许可证密钥,该字符串仅包含字母数字字符和短划线。该字符串被N个破折号分成N + 1个组。给定数字K,我们希望重新格式化字符串,使得每个组包含正好的K个字符,但第一个组可能比K短,但仍然必须包含至少一个字符。此外,必须在两个组之间插入短划线,并且所有小写字母都应转换为大写。看完题目第一时间想到的就是使用split分割后使用StringBuilder拼接。


public class LicenseKeyFormatting {
    public static String licenseKeyFormatting(String S, int K) {
        String[] str = S.split("-");
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < str.length; i++) {
        if (stringBuilder.length() <= 0) return "";
        int oth = stringBuilder.length() % K;
        int count = stringBuilder.length() / K;
        StringBuilder res = new StringBuilder();
        if (oth == 0) {
            for (int i = 0; i < count; i++) {
                String temp = stringBuilder.substring(i * K, i * K + K);
                res.append(temp + "-");
        } else {
            String head = stringBuilder.substring(0, oth);
            res.append(head + "-");
            StringBuilder stringBuilder1 = stringBuilder.delete(0, oth);
            for (int i = 0; i < count; i++) {
                String temp = stringBuilder1.substring(i * K, i * K + K);
                res.append(temp + "-");

        return res.substring(0, res.length() - 1);


 public String licenseKeyFormatting(String S, int K) {
    S = S.replaceAll("-", "").toUpperCase();
    StringBuilder sb = new StringBuilder(S);
    // Starting from the end of sb, and going backwards. 
    int i = sb.length() - K;
    while(i > 0) {
        sb.insert(i, '-');
        i = i - K;
    return sb.toString();

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