<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 dfs(string t, vector<unordered_map<char, int>>& stickCount, unordered_map<string, int>& dp) {
        if (dp.find(t) != dp.end()) {
            return dp[t];
        }
        int res = 1e9;
        for (auto& s : stickCount) {
            if (s.find(t[0]) == s.end()) continue;
            string remainT;
            unordered_map<char, int> newCount = s;
            for (char c : t) {
                if (newCount[c] > 0) {
                    newCount[c]--;
                } else {
                    remainT += c;
                }
            }
            res=min(res,1+dfs(remainT, stickCount, dp));
        }
        return dp[t] = res;
    }
    int minStickers(vector<string>& stickers, string target) {
        vector<unordered_map<char, int>> stickCount(stickers.size());
        for (int i = 0; i < stickers.size(); ++i) {
            for (char c : stickers[i]) {
                stickCount[i][c]++;
            }
        }
        unordered_map<string, int> dp;
        dp[""] = 0;
        int res=dfs(target, stickCount, dp);
        if(res>=1e9) return -1;
        return res;
    }
};
46966