<p>Given a string <code>s</code> and a dictionary of strings <code>wordDict</code>, return <code>true</code> if <code>s</code> can be segmented into a space-separated sequence of one or more dictionary words.</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;leetcode&quot;, wordDict = [&quot;leet&quot;,&quot;code&quot;]
<strong>Output:</strong> true
<strong>Explanation:</strong> Return true because &quot;leetcode&quot; can be segmented as &quot;leet code&quot;.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;applepenapple&quot;, wordDict = [&quot;apple&quot;,&quot;pen&quot;]
<strong>Output:</strong> true
<strong>Explanation:</strong> Return true because &quot;applepenapple&quot; can be segmented as &quot;apple pen apple&quot;.
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> false
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 300</code></li>
	<li><code>1 &lt;= wordDict.length &lt;= 1000</code></li>
	<li><code>1 &lt;= wordDict[i].length &lt;= 20</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>
</ul>

class Solution {
public:

    bool check( string word, vector<string>& wordDict ){
        for( auto it:wordDict ){
            if( it == word ){
                return true;
            }
        }
        return false;
    }

    // bool helperByRec(string s, vector<string>& wordDict, int start) {
    //     if( s.size() == start ) return true; // the only case where we return true
    //     string word = "";
    //     bool flag = false;
    //     for( int i=start; i<s.size(); ++i ){
    //         word += s[i];
    //         if( check( word, wordDict ) ){
    //             flag = flag || helperByRec( s, wordDict, i+1 );
    //         }
    //     }
    //     return flag;
    // }
    bool helperByRecDp(string s, vector<string>& wordDict, int start, vector<int>&dp ) {
        if( s.size() == start ) return true; // the only case where we return true
        if( dp[start] != -1 ) return dp[start];
        string word = "";
        bool flag = false;
        for( int i=start; i<s.size(); ++i ){
            word += s[i];
            if( check( word, wordDict ) ){
                flag = flag || helperByRecDp( s, wordDict, i+1, dp );
            }
        }
        return dp[start] = flag;
    }

    bool wordBreak(string s, vector<string>& wordDict) {
        vector<int>dp(s.size()+1, -1);
        return helperByRecDp(s, wordDict, 0, dp);
        // return helperByRec(s, wordDict, 0);
    }
};
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