单词中断（LeetCode==>Word Break）

题目描述：给定非空字符串s和包含非空单词列表的字典wordDict，确定是否可以将s分割为一个或多个字典中所包含的单词序列（通过空格区分）。
说明：
1.词典中的同一个词可以在分割中重复使用多次

2. 你可以假设字典不包含重复的单词
   Example1：

Input: s = "leetcode", wordDict = ["leet", "code"]
Output: true
Explanation: Return true because "leetcode" can be segmented as "leet code".

Example2：

Input: s = "applepenapple", wordDict = ["apple", "pen"]
Output: true
Explanation: Return true because "applepenapple" can be segmented as "apple pen apple".
             Note that you are allowed to reuse a dictionary word.

Example3：

Input: s = "catsandog", wordDict = ["cats", "dog", "sand", "and", "cat"]
Output: false

通过函数递归调用判断是否包含：

class Solution {
    Set<String> set=new HashSet<>();
    public boolean wordBreak(String s, List<String> wordDict) {
        if(wordDict.contains(s))
            return true;
        if(set.contains(s))
            return false;
        for(String string:wordDict){
            if(s.startsWith(string)){
                if(wordBreak(s.substring(string.length()),wordDict))
                    return true;
            }
        }
        set.add(s);
        return false;
    }
}