Problem URL: Jewels and stones

We will count all the distinct jewels and store it in a set. Then we will iterate over all the stones and check if the stone is a jewel. If it is, we will increment the count.

class Solution:
    def numJewelsInStones(self, jewels: str, stones: str) -> int:
        jewels = set(jewels)
        count = 0
        for stone in stones:
            if stone in jewels:
                count += 1
        return count

We can also count all the stones and then iterate over all the jewels and check if the jewel is in the stones. If it is, we will add the count of the jewel to the total count.

class Solution:
    def numJewelsInStones(self, jewels: str, stones: str) -> int:
        stones = collections.Counter(stones)
        count = 0
        for jewel in jewels:
            count += stones.get(jewel, 0)
        return count

Time complexity: O(n)
Space complexity: O(n)