leetcode 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.

超级无聊的一个题目，还做了好几次才对！！！其实就是先将前面几个异常的找出来，然后再规则处理。

class Solution(object):
    def licenseKeyFormatting(self, S, K):
        """
        :type S: str
        :type K: int
        :rtype: str
        """
        arr = "".join(S.upper().split('-'))        
        left = len(arr)%K        
        grouped = [arr[:left]] if left>0 else []
        for i in xrange(left, len(arr), K):            
            grouped.append(arr[i:i+K])
        return '-'.join(grouped)
        

 OR：

 def licenseKeyFormatting(self, S, K):
        """
        :type S: str
        :type K: int
        :rtype: str
        """
        S = S.replace("-", "").upper()[::-1]
        return '-'.join([S[i:i+K] for i in range(0, len(S), K)])[::-1]