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

第二个字符串包含第一个字符串的所有字母，就返回true，不一定要连续包含
只要第一个字符串中某个字母的数量 大于 第二个字符串的这个字母的数量 则返回false

C++（19ms）：

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine) {
        vector<int> magazLetters(128, 0);
        for(char m : magazine)
            magazLetters[m]++;
        for(char r : ransomNote)
            if(--magazLetters[r]<0) return false;
        return true;
    }
};