题目描述：

LeetCode 791. Custom Sort String

S and T are strings composed of lowercase letters. In S, no letter occurs more than once.

S was sorted in some custom order previously. We want to permute the characters of T so that they match the order that S was sorted. More specifically, if x occurs before y in S, then x should occur before y in the returned string.

Return any permutation of T (as a string) that satisfies this property.

Example :
Input: 
S = "cba"
T = "abcd"
Output: "cbad"
Explanation: 
"a", "b", "c" appear in S, so the order of "a", "b", "c" should be "c", "b", and "a". 
Since "d" does not appear in S, it can be at any position in T. "dcba", "cdba", "cbda" are also valid outputs.

Note:

• S has length at most 26, and no character is repeated in S.
• T has length at most 200.
• S and T consist of lowercase letters only.

题目大意：

给定字符串S和T，S中的字母互不重复。将T中的字母调整顺序，使其字母之间的先后关系与S中的字母保持一致。对于S中没有出现的字符，顺序任意。

解题思路：

统计T中各字符出现的次数

按照S的顺序将T中字符进行重排，将剩余字符排在末尾。

Python代码：

class Solution(object):
    def customSortString(self, S, T):
        """
        :type S: str
        :type T: str
        :rtype: str
        """
        counterT = collections.Counter(T)
        ans = ''
        for c in S:
            ans += c * counterT[c]
            del counterT[c]
        return ans + ''.join(k * v for k, v in counterT.items())

 

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