[LeetCode] Word Break 拆分词句

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

Note:

• The same word in the dictionary may be reused multiple times in the segmentation.
• You may assume the dictionary does not contain duplicate words.

Example 1:

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

Example 2:

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.

Example 3:

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

这道拆分词句问题是看给定的词句能分被拆分成字典里面的内容，这是一道很经典的题目，解法不止一种，考察的范围很广，属于我们必须要熟练掌握的题目。那么先来想 brute force 的解法，就拿例子1来分析，如果字典中只有两个单词，我们怎么去判断，是不是可以将原字符串s分成任意两段，然后再看分成的单词是否在字典中。注意这道题说是单词可以重复使用，所以可以分成任意段，而且字典中的单词可以有很多个，这就增加了题目的难度，很多童鞋就在这里迷失了，毫无头绪。那么，就由博主来给各位指点迷津吧（此处应有掌声