2022.3.17—–leetcode.720「终于解决」

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 public String longestWord(String[] words) {
        int n=words.length;
        Set<String> set=new HashSet<>();//存储每个字符串，便于查找
        for (int i = 0; i <n ; i++) {
            set.add(words[i]);
        }
        String ans="";
        for (int i = 0; i < n; i++) {
            //判断某个字符串是否满足条件
            if(ctn(words[i],set)){
                if(words[i].length()>ans.length())
                    ans=words[i];
                else if(words[i].length()==ans.length()){
                    if(ans.compareTo(words[i])>0)
                        ans=words[i];//字典序较小
                }
            }

        }
        return ans;
    }
    public boolean ctn(String word,Set<String> set){
        for (int j = 1; j <=word.length() ; j++) {
            if(!set.contains(word.substring(0,j)))
                return false;
        }
        return true;
    }