LeetCode771-宝石与石头

暴力(O(mn))

枚举所有的字符进行比较

使用集合(O(m+n))

public int numJewelsInStones(String jewels, String stones) {
        HashSet<Character> set = new HashSet<>();
        int res = 0;
        for (int i = 0; i < jewels.length(); i++) {
            set.add(jewels.charAt(i));
        }
        for (int i = 0; i < stones.length(); i++) {
            if (set.contains(stones.charAt(i))) res++;
        }
        return res;
    }