RansomNote.cpp

// Source : https://leetcode.com/problems/ransom-note/
// Author : Hao Chen
// Date   : 2016-08-24

/*************************************************************************************** 
 *
 * 
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) {
        unordered_map<char, int> m;
        for(int i=0; i<magazine.size(); i++) {
            m[magazine[i]]++;
        }
        for (int i=0; i<ransomNote.size(); i++) {
            char c = ransomNote[i];
            if (m[c] <=0 ) return false;
            m[c]--;
        }
        return true;
    }
};