Leetcode 383 Ransom Note

Given an arbitrary ransom note string and another string containing letters from all the magazines, write a function that will return true if the ransom note can be constructed from the magazines; otherwise, it will return false. 

Each letter in the magazine string can only be used once in your ransom note.

Note:

You may assume that both strings contain only lowercase letters.

canConstruct("a", "b") -> false
canConstruct("aa", "ab") -> false
canConstruct("aa", "aab") -> true

比较直接的思路就是把ransomNote中的字符从magazine里逐个拿出来，如果发现某个字符在magazine里面不存在也就是说明答案是False.

def canConstruct(self, ransomNote, magazine):
        """
        :type ransomNote: str
        :type magazine: str
        :rtype: bool
        """
        r = list(ransomNote)
        m = list(magazine)
        for x in r:
            if x in m:
                m.remove(x)
            else:
                return False
        return True

另外一种方法是统计一下两个str中每个字母的个数，然后相减。如果ransomCnt - magazineCnt非空，那么答案就是False.

ransomCnt = collections.Counter(ransomNote)
magazineCnt = collections.Counter(magazine)
return not ransomCnt - magazineCnt