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
class Solution(object):
    def canConstruct(self, ransomNote, magazine):
        """
        :type ransomNote: str
        :type magazine: str
        :rtype: bool
        """
        # hash cnt
        # sort merge
        s = collections.Counter(magazine)
        for c in ransomNote:
            if c in s and s[c]>0:
                s[c] -= 1
            else:
                return False
        return True

排序，类似归并思路

class Solution(object):
    def canConstruct(self, ransomNote, magazine):
        """
        :type ransomNote: str
        :type magazine: str
        :rtype: bool
        """
        # hash cnt
        # sort merge
        r = sorted(ransomNote)
        m = sorted(magazine)
        i = j = 0
        while i<len(r) and j<len(m):
            if r[i] == m[j]:
                i += 1
                j += 1
            else:
                j += 1
        return i==len(r)