Stickers to Spell Word
<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>
Bit Manipulation; Memoization; Array; Hash Table; String; Dynamic Programming; Backtracking; Bitmask
use std::collections::{HashSet, VecDeque};

impl Solution {
    pub fn min_stickers(stickers: Vec<String>, target: String) -> i32 {
        let mut q = VecDeque::new();
        q.push_back(0);
        let mut ans = 0;
        let n = target.len();
        let mut vis = HashSet::new();
        vis.insert(0);
        while !q.is_empty() {
            for _ in 0..q.len() {
                let state = q.pop_front().unwrap();
                if state == (1 << n) - 1 {
                    return ans;
                }
                for s in &stickers {
                    let mut nxt = state;
                    let mut cnt = [0; 26];
                    for &c in s.as_bytes() {
                        cnt[(c - b'a') as usize] += 1;
                    }
                    for (i, &c) in target.as_bytes().iter().enumerate() {
                        let idx = (c - b'a') as usize;
                        if (nxt & (1 << i)) == 0 && cnt[idx] > 0 {
                            nxt |= 1 << i;
                            cnt[idx] -= 1;
                        }
                    }
                    if !vis.contains(&nxt) {
                        q.push_back(nxt);
                        vis.insert(nxt);
                    }
                }
            }
            ans += 1;
        }
        -1
    }
}
