LeetCode: Ransom Note

LeetCode: 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.

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canConstruct("a", "b") -> false
canConstruct("aa", "ab") -> false
canConstruct("aa", "aab") -> true
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public class Solution {
    public boolean canConstruct(String ransomNote, String magazine) {
        Map<Character, Integer> counter = new HashMap<>();
        for (int i = 0; i < magazine.length(); i++) {
            Character c = magazine.charAt(i);
            counter.put(c, counter.getOrDefault(c, 0) + 1);
        }

        for (int i = 0; i < ransomNote.length(); i++) {
            char c = ransomNote.charAt(i);
            if (counter.getOrDefault(c, 0) <= 0) {
                return false;
            } else {
                counter.put(c, counter.get(c) - 1);
            }
        }
        return true;
    }
}