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

class Solution {
public:
bool canConstruct(string ransomNote, string magazine) {

int m[26];
memset(m,0,sizeof(m));
int cnt = 0;
for (char c : ransomNote)
{
m[c-'a']++;
cnt++;
}
for (char c : magazine)
{
if (m[c - 'a'] > 0)
{
m[c - 'a']--;
cnt--;
}
if (cnt == 0)
return true;
}
return cnt==0;

}

};

看到这道题，本来想用遍历做，后来发现自己理解错题意了，应该用map结构来做