[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

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Seen this question in a real interview before?   No

思路：

用一个map记录magazine里的字符以及个数，然后判断ransom里的字符是否能够用magazine里的表示。

bool canConstruct(string ransomNote, string magazine)
     {
         map<char, int>mpmag;
         for (auto ch : magazine)mpmag[ch]++;
         for (auto ch : ransomNote)
         {
             mpmag[ch]--;
             if (mpmag[ch] < 0)return false;             
         }
         return true;         
     }