383. Ransom Note


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

思路：

检查前面的勒索信是否可以由后面的字符串拼接而成

public boolean canConstruct(String ransomNote, String magazine) {
int[] map = new int[26];
for (int i = 0; i < magazine.length(); i++) {
map[magazine.charAt(i) - 'a']++;
}
for (int i = 0; i < ransomNote.length(); i++) {
if (map[ransomNote.charAt(i) - 'a'] > 0) {
map[ransomNote.charAt(i) - 'a']--;
} else {
return false;
}
}
return true;
}