Word Break II
<p>Given a string <code>s</code> and a dictionary of strings <code>wordDict</code>, add spaces in <code>s</code> to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in <strong>any order</strong>.</p>

<p><strong>Note</strong> that the same word in the dictionary may be reused multiple times in the segmentation.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;catsanddog&quot;, wordDict = [&quot;cat&quot;,&quot;cats&quot;,&quot;and&quot;,&quot;sand&quot;,&quot;dog&quot;]
<strong>Output:</strong> [&quot;cats and dog&quot;,&quot;cat sand dog&quot;]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;pineapplepenapple&quot;, wordDict = [&quot;apple&quot;,&quot;pen&quot;,&quot;applepen&quot;,&quot;pine&quot;,&quot;pineapple&quot;]
<strong>Output:</strong> [&quot;pine apple pen apple&quot;,&quot;pineapple pen apple&quot;,&quot;pine applepen apple&quot;]
<strong>Explanation:</strong> Note that you are allowed to reuse a dictionary word.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;catsandog&quot;, wordDict = [&quot;cats&quot;,&quot;dog&quot;,&quot;sand&quot;,&quot;and&quot;,&quot;cat&quot;]
<strong>Output:</strong> []
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 20</code></li>
	<li><code>1 &lt;= wordDict.length &lt;= 1000</code></li>
	<li><code>1 &lt;= wordDict[i].length &lt;= 10</code></li>
	<li><code>s</code> and <code>wordDict[i]</code> consist of only lowercase English letters.</li>
	<li>All the strings of <code>wordDict</code> are <strong>unique</strong>.</li>
	<li>Input is generated in a way that the length of the answer doesn&#39;t exceed&nbsp;10<sup>5</sup>.</li>
</ul>
Trie; Memoization; Array; Hash Table; String; Dynamic Programming; Backtracking
type Trie struct {
	children [26]*Trie
	isEnd    bool
}

func newTrie() *Trie {
	return &Trie{}
}
func (this *Trie) insert(word string) {
	node := this
	for _, c := range word {
		c -= 'a'
		if node.children[c] == nil {
			node.children[c] = newTrie()
		}
		node = node.children[c]
	}
	node.isEnd = true
}
func (this *Trie) search(word string) bool {
	node := this
	for _, c := range word {
		c -= 'a'
		if node.children[c] == nil {
			return false
		}
		node = node.children[c]
	}
	return node.isEnd
}

func wordBreak(s string, wordDict []string) []string {
	trie := newTrie()
	for _, w := range wordDict {
		trie.insert(w)
	}
	var dfs func(string) [][]string
	dfs = func(s string) [][]string {
		res := [][]string{}
		if len(s) == 0 {
			res = append(res, []string{})
			return res
		}
		for i := 1; i <= len(s); i++ {
			if trie.search(s[:i]) {
				for _, v := range dfs(s[i:]) {
					v = append([]string{s[:i]}, v...)
					res = append(res, v)
				}
			}
		}
		return res
	}
	res := dfs(s)
	ans := []string{}
	for _, v := range res {
		ans = append(ans, strings.Join(v, " "))
	}
	return ans
}