May-3 2020 Challenge

3.Ransom Note

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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

Solution in Java:

public class Solution {
    public boolean canConstruct(String ransomNote, String magazine) {
        Map<Character, Integer> freq = new HashMap<>();
        for(char c: magazine.toCharArray()) {
            if(freq.containsKey(c)) {
                freq.put(c, freq.get(c) + 1);
            } else {
                freq.put(c, 1);
            }
        }
        for(char c: ransomNote.toCharArray()) {
            if (freq.containsKey(c)) {
                if(freq.get(c) > 1) {
                    freq.put(c, freq.get(c) - 1);
                } else {
                    freq.remove(c);
                }
            }else{
                return false;
            }
        }
        return true;
    }
}