leetcode之Ransom Note

题目描述：


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) {
        /*第一种方法
        if(ransomNote.size() > magazine.size()){
            return false;
        }
        for(int i = 0; i<ransomNote.size() ;){
            char ch = ransomNote[i];
            std::size_t found = magazine.find(ch); 
            if(found != std::string::npos){
                ransomNote.erase(i,1);
                magazine.erase(found,1);
                continue;
            }
            i++;
        }
        if(ransomNote.length() == 0)
            return true;
        else
            return false;
    }*//*第二种检测方法*/
        int* arr = new int[26];
        for(int i=0;i<26;i++){
            arr[i] = 0;
        }
        for(int i=0;i<magazine.length();i++)
        {
            char c = magazine[i];
            arr[c-'a']++;
        }
        
        for(int i=0;i<ransomNote.length();i++)
        {
            char c = ransomNote[i];
            arr[c-'a']--;
            if(arr[c-'a']<0) 
                return false;
        }
        
        return true;
    }
};