Tags: "leetcode", access_time 1-min read

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Ransom Note

Created: May 3, 2020 by [lek-tin]

Last updated: May 3, 2020

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.


You may assume that both strings contain only lowercase letters.


canConstruct("a", "b") -> false
canConstruct("aa", "ab") -> false
canConstruct("aa", "aab") -> true



class Solution {
    public boolean canConstruct(String ransomNote, String magazine) {
        HashMap<Character, Integer> rnCounter = new HashMap<Character, Integer>();
        HashMap<Character, Integer> magCounter = new HashMap<Character, Integer>();

        for (Character c: ransomNote.toCharArray()) {
            rnCounter.put(c, rnCounter.getOrDefault(c, 0)+1);
        for (Character c: magazine.toCharArray()) {
            magCounter.put(c, magCounter.getOrDefault(c, 0)+1);

        Iterator<Map.Entry<Character, Integer>> it = rnCounter.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<Character, Integer> entry = it.next();
            if ( !magCounter.containsKey(entry.getKey()) ) {
                return false;
            if ( magCounter.get(entry.getKey()) < entry.getValue() ) {
                return false;

        return true;