G面经Prepare: Search word delete sequence in dictionary

给一个单词一个字典，每次删除单词里任一个字母直到剩下一个字母，形成一个序列，比如office->offce->ofce->ofc->oc->c。问是否字典里存在一个这种序列

 package checkDictExistSequence;
 import java.util.*;

 public class Solution {
     HashSet<String> dict = new HashSet<String>();

     public String check(String[] arr, String word) {
         for (String str : arr)
             dict.add(str);
         if (checkSeq(new StringBuffer(word))) return "true";
         return "false";
     }

     public boolean checkSeq(StringBuffer sb) {
         if (sb.length() == 1) return true;
         for (int i=0; i<=sb.length()-1; i++) {
             char cur = sb.charAt(i);
             sb.deleteCharAt(i);
             if (dict.contains(sb.toString())) {
                 if (checkSeq(sb)) return true;
             }
             sb.insert(i, cur);
         }
         return false;
     }

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Solution sol = new Solution();
         System.out.println(sol.check(new String[]{"offce", "ofce", "ofc", "oc", "c"}, "office"));
     }

 }