771. Jewels and Stones

Description

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
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Note:

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

Solution

HashSet, time O(n), space O(n)

class Solution {
    public int numJewelsInStones(String J, String S) {
        if (J == null || S == null) {
            return -1;
        }
        
        Set<Character> jewels = new HashSet<>();
        for (int i = 0; i < J.length(); ++i) {
            jewels.add(J.charAt(i));
        }
        
        int count = 0;
        for (int i = 0; i < S.length(); ++i) {
            if (jewels.contains(S.charAt(i))) {
                ++count;
            }
        }
        
        return count;
    }
}