Java編程題目-12：字符串的construct

題目要求：

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

原題鏈接：請戳這裏
解決代碼如下：

public class Solution {
    public boolean canConstruct(String ransomNote, String magazine) {
        ArrayList<Character> ranList = getListFromArray(ransomNote);
        ArrayList<Character> magList = getListFromArray(magazine);
        // 循環從ransomNote中取出字符
        for(int i=0;i<ranList.size();i++){
            char c = ranList.get(i);
            if(magList.contains(c)){
                magList.remove(magList.indexOf(c));// *比對之後刪掉該字符
                continue;
            }else{
                return false;
            }
        }
        return true;
    }
    // 將string轉成list
    public ArrayList<Character> getListFromArray(String string){
        ArrayList<Character> list = new ArrayList<Character>();
        char[] strArr = string.toCharArray();
        for (char c : strArr) {
            list.add(c);
        }
        return list;
    }
}

---

我的思路：
1. 從ransomNote中逐個取出字符
2. 再到magazine中去確認是否含有該字符
3. 如果magazine中包含該字符，則刪掉magazine中的這個字符
4. 如果magazine中不含該字符，則返回false

爲什麼要刪掉magazine中的對應字符？因爲假如說ransomNote爲“aaagbfrd”，而magazine爲“aabgefdrtg“時，針對字符‘a’就會出現錯誤判斷，當判斷ransomNote中第三個‘a’時，實際應該是false，但是magazine中還是有‘a’與之對應，故會返回錯誤值true。