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

題目含義：判斷給定字符串能否由另一字符串中字符組合生成

 1     public boolean canConstruct(String ransomNote, String magazine) {
 2         Map<Character,Integer> letterMap = new
 
 HashMap<>();
 3         for (Character c:magazine.toCharArray())
 4         {
 5             letterMap.put(c,letterMap.getOrDefault(c,0)+1);
 6         }
 7         
 8         for (Character c:ransomNote.toCharArray())
 9         {
10             int count = letterMap.getOrDefault(c,0);
11             if
 
 (count<=0) return false;
12             letterMap.put(c,--count);
13         }
14         return true;        
15     }

383. Ransom Note