<p>You are given a string <code>s</code> and an array of strings <code>words</code>. All the strings of <code>words</code> are of <strong>the same length</strong>.</p>

<p>A <strong>concatenated string</strong> is a string that exactly contains all the strings of any permutation of <code>words</code> concatenated.</p>

<ul>
	<li>For example, if <code>words = [&quot;ab&quot;,&quot;cd&quot;,&quot;ef&quot;]</code>, then <code>&quot;abcdef&quot;</code>, <code>&quot;abefcd&quot;</code>, <code>&quot;cdabef&quot;</code>, <code>&quot;cdefab&quot;</code>, <code>&quot;efabcd&quot;</code>, and <code>&quot;efcdab&quot;</code> are all concatenated strings. <code>&quot;acdbef&quot;</code> is not a concatenated string because it is not the concatenation of any permutation of <code>words</code>.</li>
</ul>

<p>Return an array of <em>the starting indices</em> of all the concatenated substrings in <code>s</code>. You can return the answer in <strong>any order</strong>.</p>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;barfoothefoobarman&quot;, words = [&quot;foo&quot;,&quot;bar&quot;]</span></p>

<p><strong>Output:</strong> <span class="example-io">[0,9]</span></p>

<p><strong>Explanation:</strong></p>

<p>The substring starting at 0 is <code>&quot;barfoo&quot;</code>. It is the concatenation of <code>[&quot;bar&quot;,&quot;foo&quot;]</code> which is a permutation of <code>words</code>.<br />
The substring starting at 9 is <code>&quot;foobar&quot;</code>. It is the concatenation of <code>[&quot;foo&quot;,&quot;bar&quot;]</code> which is a permutation of <code>words</code>.</p>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;wordgoodgoodgoodbestword&quot;, words = [&quot;word&quot;,&quot;good&quot;,&quot;best&quot;,&quot;word&quot;]</span></p>

<p><strong>Output:</strong> <span class="example-io">[]</span></p>

<p><strong>Explanation:</strong></p>

<p>There is no concatenated substring.</p>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;barfoofoobarthefoobarman&quot;, words = [&quot;bar&quot;,&quot;foo&quot;,&quot;the&quot;]</span></p>

<p><strong>Output:</strong> <span class="example-io">[6,9,12]</span></p>

<p><strong>Explanation:</strong></p>

<p>The substring starting at 6 is <code>&quot;foobarthe&quot;</code>. It is the concatenation of <code>[&quot;foo&quot;,&quot;bar&quot;,&quot;the&quot;]</code>.<br />
The substring starting at 9 is <code>&quot;barthefoo&quot;</code>. It is the concatenation of <code>[&quot;bar&quot;,&quot;the&quot;,&quot;foo&quot;]</code>.<br />
The substring starting at 12 is <code>&quot;thefoobar&quot;</code>. It is the concatenation of <code>[&quot;the&quot;,&quot;foo&quot;,&quot;bar&quot;]</code>.</p>
</div>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= words.length &lt;= 5000</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 30</code></li>
	<li><code>s</code> and <code>words[i]</code> consist of lowercase English letters.</li>
</ul>

// const auto fastIO = []() {
//     std::ios::sync_with_stdio(false);
//     std::cin.tie(nullptr);
//     std::cout.tie(nullptr);
//     return 0;
// }();


class Solution {
public:

    inline bool equal(auto s1, auto e1, auto s2) {
        while (s1 != e1) {
            if (*s1 != *s2) {
                return false;
            }
            ++s1;
            ++s2;
        }
        return true;
    }

    inline auto findAndMark(auto words_b, auto& words_e, auto s_begin) {
        while (words_b != words_e) {
            if (equal(words_b->begin(), words_b->end(), s_begin)) {
                --words_e;
                std::swap(*words_b, *words_e);
                return true;
            } 
            ++words_b;
        }
        return false;
    }
    inline bool is_concatenated(auto begin, auto end, auto words_b, auto words_e, const auto word_size, const auto size) {
        // std::distance(begin, end) == word_size * words.size()
        while (begin != end) {
            if (findAndMark(words_b, words_e, begin)) {
                begin += word_size;
            } else {
                return false;
            }
        }
        return true;
    }
    inline std::vector<int> findSubstring(const std::string& s, std::vector<std::string>& words) {
        const auto size = words.size();
        const auto s_size = s.size();
        const auto word_size = words[0].size();
        const auto words_size = word_size * size;

        if (s_size < words_size) {
            return {};
        }
        auto ret = std::vector<int>{};
        ret.reserve(8);

        auto valid = std::set<std::deque<char>>{};
        auto not_valid = std::set<std::deque<char>>{};


        auto words_b = words.begin();
        auto words_e = words.end();
        auto s_b = s.begin();
        auto s_e = s.end();

        auto deque = std::deque<char>(s_b, s_b + words_size - 1);
        s_b += words_size - 1;
        auto first = s_b;

        while (s_b != s_e) {
            deque.push_back(*s_b);
            if (valid.contains(deque)) {
                ret.push_back(std::distance(first, s_b));
            } else if (not_valid.contains(deque)) {
                // pass
            } else if (is_concatenated(deque.begin(), deque.end(), words_b, words_e, word_size, size)) {
                ret.push_back(std::distance(first, s_b));
                valid.insert(deque);
            } else {
                not_valid.insert(deque);
            }
            ++s_b;
            deque.pop_front();
        }
        return ret;
    }
};
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