【Leetcode】Ransom Note

题目链接：https://leetcode.com/problems/ransom-note/

题目：

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

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思路：
题意是让你判断 前面字符串能否由后面字符串的部分字符构造出来。
因为只有小写字母，用数组代替map存储magazine每个字符出现的次数，遍历ransom note 每个字符并判断。
easy
算法：
public boolean canConstruct(String ransomNote, String magazine) {
int[] map = new int[26];
for(char mc:magazine.toCharArray()){
map[mc-'a']++;
}

for(char rc:ransomNote.toCharArray()){
if(map[rc-'a']>0){
map[rc-'a']--;
}else{
return false;
}
}
return true;

}