383. Ransom Note

原题链接：https://leetcode.com/problems/ransom-note/

原题：

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") -> falsecanConstruct("aa", "ab") -> falsecanConstruct("aa", "aab") -> true

题意：
给你两个字符串1和2，要去你判断能否用字符串2里面的字母组成字符串1，要求字符串2里面的字母一个只能用一次，能则return true 反之return false，给的字母都是小写字母。

思路：
用一个int数组保存26个小写字母在字符串2的出现次数，然后开始遍历字符串1，然后每次遇到一个字母，判断一次“库存”，不够，择return false，够则库存-1；遍历完成后，发现都够，则return true。

AC代码

class Solution {public:    bool canConstruct(string ransomNote, string magazine) {        int b[26]={0};        for(char s:magazine){            b[s-'a']++;        }        for(char s:ransomNote){            if(b[s-'a']==0) return false;            b[s-'a']--;        }        return true;    }};