字符串按词典分割

题目原型：

Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or

 more dictionary words.

For example, given
s = "leetcode",
dict = ["leet", "code"].

Return true because "leetcode" can be segmented as "leet code".

思路：

可以考虑用动态规划，用f(i,j)表示字符串S从i到j的子串是否可分割，

则有：f(0,n) = f(0,i) && f(i,n)，然后f(0,i)和f(i,n)又可以继续分割。

public boolean wordBreak(String s, Set<String> dict) {if(dict.size()==0)return false;if(s.equals("")||s==null)return true;ArrayList<Integer> list = new ArrayList<Integer>();//存放能够被检索的字符串的位置int len = s.length();String str,strtemp;for(int i = len-1;i>=0;i--){str = s.substring(i);if(dict.contains(str)){list.add(i);}else{//如果词典中不包含的话就在已经分割的字符串中找，比如字符串是“hello”，而词典中有“hel”和“lo”,那么就先匹配“lo”，再匹配“hel”for(Integer index : list){strtemp = s.substring(i, index);if(dict.contains(strtemp)){list.add(i);break;}}}}if(list.size()>0&&list.get(list.size()-1)==0)return true;elsereturn false;    }