【Leetcode】482. License Key Formatting

482. License Key Formatting

Now you are given a string S, which represents a software license key which we would like to format. The string S is composed of alphanumerical characters and dashes. The dashes split the alphanumerical characters within the string into groups. (i.e. if there are M dashes, the string is split into M+1 groups). The dashes in the given string are possibly misplaced.

We want each group of characters to be of length K (except for possibly the first group, which could be shorter, but still must contain at least one character). To satisfy this requirement, we will reinsert dashes. Additionally, all the lower case letters in the string must be converted to upper case.

So, you are given a non-empty string S, representing a license key to format, and an integer K. And you need to return the license key formatted according to the description above.

Example 1:

Input: S = "2-4A0r7-4k", K = 4

Output: "24A0-R74K"

Explanation: The string S has been split into two parts, each part has 4 characters.

Example 2:

Input: S = "2-4A0r7-4k", K = 3

Output: "24-A0R-74K"

Explanation: The string S has been split into three parts, each part has 3 characters except the first part as it could be shorter as said above.

Note:

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.

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题目大意：题目大概说的是给你一个字符串，需要你把字符串全部转换成固定的格式。其中，给你一个整数K，将给定的字符串中的字符每K个为一组，之间用“-”分隔。其中第一个字符的长度可以小于K。

思路分析：

预处理：想法很简单先把字符串中“-”全部去掉，然后把字符串中的字符转换为大写的形式。

思路一：

利用JAVA中重载的“+”不断地拼凑char + String = String

缺点：每次拼接都创建了一个新的String对象，严重影响了算法效率。

思路二：

创建一个char[],将计算好的输入字符串对应的字母填进去，最后将char[]->String输出就行了

优点：只需要创建一个char[]，提高了执行速度。

代码：

思路一：

public String licenseKeyFormatting(String S, int K) {
        S = S.replace("-","");
        if(S.length() == 0){
            return "";
        }
        S = S.toUpperCase();
        String res = "";
        int count=0;
        while(S.length()-1-count>=0){
            for(int i=0;i<K&&S.length()-1-count>=0;i++){
                res = S.charAt(S.length()-1-count)+res;
                count++;
            }
            res = "-"+res;
        }
        return res.substring(1,res.length());
    }

思路二：

public String licenseKeyFormatting(String S, int K) {
        S = S.replace("-","");
        if(S.length() == 0){
            return "";
        }
        S = S.toUpperCase();
        char[] res = new char[S.length()+(int)Math.ceil(1.0*S.length()/K)-1];
        int aLength = res.length-1;
        int count=0;
        while(aLength>=K){
            for(int i=0;i<K;i++){
                res[aLength--] = S.charAt(S.length()-1-count++);
            }
            res[aLength--]='-';
        }
        for(int i=0;i<K&&aLength>=0;i++){
            res[aLength--] = S.charAt(S.length()-1-count++);
        }
        return new String(res);
    }

运行结果：

思路一：

思路二：