[Leetcode] 140. Work Break II

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Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.

Return all such possible sentences.

For example, given
s = "catsanddog",
dict = ["cat", "cats", "and", "sand", "dog"].

A solution is ["cats and dog", "cat sand dog"].

这道还是用NP套路，for循环加backtracking，但是这么做会超时。

import java.util.ArrayList;public class Solution {    public List<String> wordBreak(String s, Set<String> dict) {        ArrayList<String> result = new ArrayList<String>();        if(s == null || s.length() == 0) return result;        ArrayList<String> list = new ArrayList<String>();        helper(s, dict, result, 0, list);        return result;    }    private void helper(String s, Set<String> dict, ArrayList<String> result, int start, ArrayList<String> list){        if(start == s.length()){            StringBuffer sb = new StringBuffer();            for(int i = 0; i < list.size() - 1; i++){                sb.append(list.get(i) + " ");            }            sb.append(list.get(list.size() - 1));            result.add(sb.toString());            return;        }        for(int i = start; i < s.length(); i++){            String cur = s.substring(start, i + 1);            if(dict.contains(cur)){                list.add(cur);                helper(s, dict, result, i + 1, list);                list.remove(list.size() - 1);            }        }    }}

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