Leetcode 791. Custom Sort String

文章作者：Tyan
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1. Description

2. Solution

解析：Version 1，Python3 3.6之后字典是有序的，因此先根据order构建一个有序字典，遍历str，将在order中的字符放到字典中，不存在的放到最终结果的前面，最后遍历字典，合并字符串。Version 2利用python自带的排序。

• Version 1

class Solution:
    def customSortString(self, order: str, str: str) -> str:
        dictionary = {ch: [] for ch in order}
        ans = ''
        for ch in str:
            if ch in dictionary:
                dictionary[ch].append(ch)
            else:
                ans += ch
        for val in dictionary.values():
            ans += ''.join(val)
        return ans

• Version 2

class Solution:
    def customSortString(self, order: str, str: str) -> str:
        mapping = {}
        for index, val in enumerate(order):
            mapping[val] = index
        s1 = ''
        s2 = ''
        for ch in str:
            if ch in mapping:
                s1 += ch
            else:
                s2 += ch
        return ''.join(sorted(s1, key=lambda ch: mapping[ch])) + s2

Reference

1. https://leetcode.com/problems/custom-sort-string/