Check If String Is a Prefix of Array

给一个字符串s和一个字符串组, 求这个字符串组所组成的prefix字符串有没有s.

class Solution {
    public boolean isPrefixString(String s, String[] words) {
        Set<String> set = new HashSet<>();
        int n = words.length;
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < n; i++)
        { 
            sb.append(words[i]);
            set.add(sb.toString());
        }
        return set.contains(s);
    }
}