LeetCode 1684. 统计一致字符串的数目（哈希）

示例 1：
输入：allowed = "ab", words = ["ad","bd","aaab","baa","badab"]
输出：2
解释：字符串 "aaab" 和 "baa" 都是一致字符串，因为它们只包含字符 'a' 和 'b' 。

示例 2：
输入：allowed = "abc", words = ["a","b","c","ab","ac","bc","abc"]
输出：7
解释：所有字符串都是一致的。

示例 3：
输入：allowed = "cad", words = ["cc","acd","b","ba","bac","bad","ac","d"]
输出：4
解释：字符串 "cc"，"acd"，"ac" 和 "d" 是一致字符串。
 
提示：
1 <= words.length <= 104
1 <= allowed.length <= 26
1 <= words[i].length <= 10
allowed 中的字符 互不相同 。
words[i] 和 allowed 只包含小写英文字母。

class Solution {
public:
    int countConsistentStrings(string allowed, vector<string>& words) {
        unordered_set<char> s(allowed.begin(), allowed.end());
        int ans = 0;
        for(int i = 0; i < words.size(); ++i)
        {
            bool flag = true;
            for(int j = 0; j < words[i].size(); ++j)
            {
                if(!s.count(words[i][j]))
                {
                    flag = false;
                    break;
                }
            }
            if(flag)
                ans++;
        }
        return ans;
    }
};