Ransom Note

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  
public class Solution {  
    public boolean canConstruct(String ransomNote, String magazine) {
        if (ransomNote == null || ransomNote.length() == 0) {
            return true;
        }
        if (magazine == null || magazine.length() == 0) {
            return false;
        }

        int[] chars = new int[26];
        for (int i = 0; i < magazine.length(); i++) {
            chars[magazine.charAt(i) - 'a']++;
        }

        for (int i = 0; i < ransomNote.length(); i++) {
            char c = ransomNote.charAt(i);
            chars[c - 'a']--;

            if (chars[c - 'a'] < 0) {
                return false;
            }
        }

        return true;
    }
}

Hope this helps,
Michael