public void insert(TrieNode root, String target) {
    // sanity check.Trietar
    char[] targetArr =  target.toCharArray();
    TrieNode cur = root;
    for (int i = 0; i < target.length(); i++) {
        TrieNode next = cur.children.get(target.charAt(i));
        if (next == null) {
            next = new TrieNode();
            cur.children.put(target.CharAt(i), next);
        }
        cur = next;
        cur.count++;
    }
    cur.isEnd = true;
}