771. Jewels and Stones

771. Jewels and Stones

Question

You’re given strings J representing the types of stones that are jewels, and S representing the stones you have. Each character in S is 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.

Solution

• Method 1: HashSet

  class Solution {
      public int numJewelsInStones(String J, String S) {
          Set<Character> set = new HashSet<>();
          for(char c : J.toCharArray()){
              set.add(c);
          }
          int res = 0;
          for(char c : S.toCharArray()){
              if(set.contains(c)) res++;
          }
          return res;
      }
  }
  

Amazon session

class Solution {
    public int numJewelsInStones(String J, String S) {
        Set<Character> jewels = new HashSet<>();
        for(char c : J.toCharArray()){
            jewels.add(c);
        }
        int result = 0;
        for(char c : S.toCharArray()){
            if(jewels.contains(c))
                result++;
        }
        return result;
    }
}