Leetcode 771. Jewels and Stones

You're given strings J representing the types of stones that are jewels, and S representing the stones you have.  Each character in Sis a type of stone you have.  You want to know how many of the stones you have are also jewels.

The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so "a" is considered a different type of stone from "A".

Example 1:

Input: J = "aA", S = "aAAbbbb"
Output: 3

Example 2:

Input: J = "z", S = "ZZ"
Output: 0

Note:

• S and J will consist of letters and have length at most 50.
• The characters in J are distinct.

Code (Java):

class Solution {
    public int numJewelsInStones(String J, String S) {
        if (J == null || J.length() == 0 || S == null || S.length() == 0) {
            return 0;
        }
        
        int ans = 0;
        
        boolean[] dictS = new boolean[26];
        boolean[] dictL = new boolean[26];
        
        // step 1: pre-process the string J and put chars into the dict
        //
        for (int i = 0; i < J.length(); i++) {
            char c = J.charAt(i);
            if (c >= 'a' && c <= 'z') {
                dictS[c - 'a'] = true;
            } else {
                dictL[c - 'A'] = true;
            }
        }
        
        // step 2: check each char in S and see if it's in the dict
        //
        for (int i = 0; i < S.length(); i++) {
            char c = S.charAt(i);
            if (c >= 'a' && c <= 'z' && dictS[c - 'a']) {
                ans++;
            } else if (c >= 'A' && c <= 'Z' && dictL[c - 'A']) {
                ans++;
            }
        }
        
        return ans;
    }
}