leetcode 139. Word Break

Seawolf

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

class Solution {
    HashMap<String,Boolean> map = new HashMap<>();
    public boolean wordBreak(String s, List<String> wordDict) {
        return help(s, wordDict);
    }
    
    public boolean help(String s, List<String> Dict){
        if(map.containsKey(s)) return map.get(s);
        if(Dict.contains(s)) {
            map.put(s,true);
            return true;
        }
        
        for(int i = 1; i< s.length() ; i++){
            String left = s.substring(0,i);
            String right = s.substring(i);
            if(Dict.contains(right) && help(left,Dict)) {
                map.put(s,true);
                return true;
            }
        }
        
        map.put(s,false);
        return false;
    }
}