<p>A <strong>transformation sequence</strong> from word <code>beginWord</code> to word <code>endWord</code> using a dictionary <code>wordList</code> is a sequence of words <code>beginWord -&gt; s<sub>1</sub> -&gt; s<sub>2</sub> -&gt; ... -&gt; s<sub>k</sub></code> such that:</p>

<ul>
	<li>Every adjacent pair of words differs by a single letter.</li>
	<li>Every <code>s<sub>i</sub></code> for <code>1 &lt;= i &lt;= k</code> is in <code>wordList</code>. Note that <code>beginWord</code> does not need to be in <code>wordList</code>.</li>
	<li><code>s<sub>k</sub> == endWord</code></li>
</ul>

<p>Given two words, <code>beginWord</code> and <code>endWord</code>, and a dictionary <code>wordList</code>, return <em>all the <strong>shortest transformation sequences</strong> from</em> <code>beginWord</code> <em>to</em> <code>endWord</code><em>, or an empty list if no such sequence exists. Each sequence should be returned as a list of the words </em><code>[beginWord, s<sub>1</sub>, s<sub>2</sub>, ..., s<sub>k</sub>]</code>.</p>

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

<pre>
<strong>Input:</strong> beginWord = &quot;hit&quot;, endWord = &quot;cog&quot;, wordList = [&quot;hot&quot;,&quot;dot&quot;,&quot;dog&quot;,&quot;lot&quot;,&quot;log&quot;,&quot;cog&quot;]
<strong>Output:</strong> [[&quot;hit&quot;,&quot;hot&quot;,&quot;dot&quot;,&quot;dog&quot;,&quot;cog&quot;],[&quot;hit&quot;,&quot;hot&quot;,&quot;lot&quot;,&quot;log&quot;,&quot;cog&quot;]]
<strong>Explanation:</strong>&nbsp;There are 2 shortest transformation sequences:
&quot;hit&quot; -&gt; &quot;hot&quot; -&gt; &quot;dot&quot; -&gt; &quot;dog&quot; -&gt; &quot;cog&quot;
&quot;hit&quot; -&gt; &quot;hot&quot; -&gt; &quot;lot&quot; -&gt; &quot;log&quot; -&gt; &quot;cog&quot;
</pre>

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

<pre>
<strong>Input:</strong> beginWord = &quot;hit&quot;, endWord = &quot;cog&quot;, wordList = [&quot;hot&quot;,&quot;dot&quot;,&quot;dog&quot;,&quot;lot&quot;,&quot;log&quot;]
<strong>Output:</strong> []
<strong>Explanation:</strong> The endWord &quot;cog&quot; is not in wordList, therefore there is no valid transformation sequence.
</pre>

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

<ul>
	<li><code>1 &lt;= beginWord.length &lt;= 5</code></li>
	<li><code>endWord.length == beginWord.length</code></li>
	<li><code>1 &lt;= wordList.length &lt;= 500</code></li>
	<li><code>wordList[i].length == beginWord.length</code></li>
	<li><code>beginWord</code>, <code>endWord</code>, and <code>wordList[i]</code> consist of lowercase English letters.</li>
	<li><code>beginWord != endWord</code></li>
	<li>All the words in <code>wordList</code> are <strong>unique</strong>.</li>
	<li>The <strong>sum</strong> of all shortest transformation sequences does not exceed <code>10<sup>5</sup></code>.</li>
</ul>

class Solution {
public:
    std::vector<int> adj[505];
    int dis[505];
    std::string start;
    std::vector<int> current;

    inline bool adjacent(const string& a, const string& b) {
        bool is_diff = false;
        for (int i = 0; i < a.size(); i++) {
            if (a[i] != b[i]) {
                if (is_diff) {
                    return false;
                }
                is_diff = true;
            }
        }
        return is_diff;
    }

    std::vector<std::string> rev(std::vector<int> &v, std::vector<std::string>& wordList) {
        std::vector<std::string> r;
        r.push_back(start);
        for (auto it = v.rbegin(); it != v.rend(); ++it)
            r.push_back(wordList[*it]);
        return r;
    }

    void recurse(int node, std::vector<std::vector<std::string>> &paths, std::vector<std::string>& wordList) {
        current.push_back(node);
        if (dis[node] == 0) {
            paths.push_back(rev(current, wordList));
        } else {
            for (int check : adj[node]) {
                if (dis[check] + 1 == dis[node]) {
                    recurse(check, paths, wordList);
                }
            }
        }
        current.pop_back();
    }

    vector<vector<string>> findLadders(string beginWord, string endWord, vector<string>& wordList) {
        int end_index = -1;
        start = beginWord;

        memset(dis, -1, sizeof dis);

        std::queue<int> q;

        for (int i = 0; i < wordList.size(); i++) {
            adj[i].clear();
        }

        for (int i = 0; i < wordList.size(); i++) {
            if (wordList[i] == endWord) {
                end_index = i;
            }

            if (adjacent(beginWord, wordList[i])) {
                q.push(i);
                dis[i] = 0;
            }

            for (int j = i + 1; j < wordList.size(); j++) {
                if (adjacent(wordList[i], wordList[j])) {
                    adj[i].push_back(j);
                    adj[j].push_back(i);
                }
            }
        }

        if (end_index == -1) {
            return {};
        }

        while (q.size()) {
            int node = q.front(); q.pop();
            for (int check : adj[node]) {
                if (dis[check] != -1) continue;
                dis[check] = dis[node] + 1;
                q.push(check);
            }
        }

        std::vector<std::vector<std::string>> paths;
        recurse(end_index, paths, wordList);

        return paths;
    }
};
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