LeetCode | Word Break II

原题描述：https://oj.leetcode.com/problems/word-break-ii/

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"].

解题思路：

动态规划+DFS

实现代码：

/**
 * LeetCode | Word Break II
 * @author wzystal@gmail.com
 */
public class Solution {
	List<String> records = new ArrayList<String>();

	public List<String> wordBreak(String s, Set<String> dict) {
		if (canBreak(s, dict)) {
			dfsSearch(s, dict, "");
		}
		return records;
	}

	private boolean canBreak(String s, Set<String> dict) {
		if (s == null || s.length() == 0 || dict == null || dict.size()==0)
			return false;
		int len = s.length();
		boolean[] can = new boolean[len + 1];
		can[0] = true;
		for (int i = 1; i <= len; i++) {
			for (int j = 0; j < i; j++) {
				if (can[j] && dict.contains(s.substring(j, i))) {
					can[i] = true;
					break;
				}
			}
		}
		return can[len];
	}

	private void dfsSearch(String str, Set<String> dict, String result) {
		int len = str.length();
		if (len == 0) {
			records.add(result);
		}
		for (int i = 0; i <= len; i++) {
			String sub = str.substring(0,i);
			if(dict.contains(sub)){
				int curLen = result.length();
				if(!result.equals("")){
					result += " ";
				}
				result += sub;
				dfsSearch(str.substring(i), dict, result);
				result = result.substring(0, curLen);
			}
		}
	}
}