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"));
}

}