<p>We are given <code>n</code> different types of <code>stickers</code>. Each sticker has a lowercase English word on it.</p>

<p>You would like to spell out the given string <code>target</code> by cutting individual letters from your collection of stickers and rearranging them. You can use each sticker more than once if you want, and you have infinite quantities of each sticker.</p>

<p>Return <em>the minimum number of stickers that you need to spell out </em><code>target</code>. If the task is impossible, return <code>-1</code>.</p>

<p><strong>Note:</strong> In all test cases, all words were chosen randomly from the <code>1000</code> most common US English words, and <code>target</code> was chosen as a concatenation of two random words.</p>

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

<pre>
<strong>Input:</strong> stickers = [&quot;with&quot;,&quot;example&quot;,&quot;science&quot;], target = &quot;thehat&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong>
We can use 2 &quot;with&quot; stickers, and 1 &quot;example&quot; sticker.
After cutting and rearrange the letters of those stickers, we can form the target &quot;thehat&quot;.
Also, this is the minimum number of stickers necessary to form the target string.
</pre>

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

<pre>
<strong>Input:</strong> stickers = [&quot;notice&quot;,&quot;possible&quot;], target = &quot;basicbasic&quot;
<strong>Output:</strong> -1
Explanation:
We cannot form the target &quot;basicbasic&quot; from cutting letters from the given stickers.
</pre>

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

<ul>
	<li><code>n == stickers.length</code></li>
	<li><code>1 &lt;= n &lt;= 50</code></li>
	<li><code>1 &lt;= stickers[i].length &lt;= 10</code></li>
	<li><code>1 &lt;= target.length &lt;= 15</code></li>
	<li><code>stickers[i]</code> and <code>target</code> consist of lowercase English letters.</li>
</ul>

class Solution {
public:
    int helper(int index,int mask,vector<string>& stickers,string target,vector<vector<int>>&dp)
    {
        if(mask==0)
        return 0;

        if(index==stickers.size())
        return 1e8;

        if(dp[index][mask]!=-1)
        return dp[index][mask];

        vector<int> freq(26,0);
        for(int i=0;i<stickers[index].length();i++)
        {
            freq[stickers[index][i]-'a']++;
        }

        bool change=false;
        int ans=1e8;
        int temp_mask=mask;
        for(int i=0;i<target.size();i++)
        {
            if(freq[target[i]-'a']>0 && (temp_mask & (1<<i)))
            {
                change=true;
                freq[target[i]-'a']--;
                temp_mask=temp_mask ^ (1<<i);
            }
        }
        if(change)
        {
            ans=min(ans,1+helper(index,temp_mask,stickers,target,dp));
        }
        ans=min(ans,helper(index+1,mask,stickers,target,dp));

        return dp[index][mask]=ans;


    }
    int minStickers(vector<string>& stickers, string target) {
        int n=target.size();
        vector<vector<int>> dp(stickers.size(),vector<int>(1<<n,-1));
        int mask=(1<<n)-1;

        int val=helper(0,mask,stickers,target,dp);
        if(val==1e8)
        return -1;

        return val;
        
    }
};
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