383. Ransom Note

// LeetCode URL: https://leetcode.com/problems/ransom-note/
/**
 * Time Complexity: O(R + M)
 *
 * Space Complexity: O(26) ~= O(1)
 *
 * R = Length of ransomNote string. M = Length of magazine string.
 */
class Solution {
    public boolean canConstruct(String ransomNote, String magazine) {
        if (ransomNote == null || magazine == null || magazine.length() < ransomNote.length()) {
            return false;
        }
        if (ransomNote.length() == 0) {
            return true;
        }

        int[] charCount = new int[26];
        for (char c : magazine.toCharArray()) {
            charCount[c - 'a']++;
        }

        for (char c : ransomNote.toCharArray()) {
            if (charCount[c - 'a'] == 0) {
                return false;
            }
            charCount[c - 'a']--;
        }

        return true;
    }
}