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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题目，如果前面的字符串中的字母后面一个字符中都有，而且个数不小于前面一个字符串则返回true，否则返回false

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine) {
        map<char, int> map;
        for (auto &e : ransomNote)
        {
            ++map[e];
        }
        for (auto &e : magazine)
        {
            if (map.find(e) != map.end())
            {
                if (--map[e] == 0)
                {
                    map.erase(e);
                }
            }
        }
        return !map.size();
    }
};