<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:

    unordered_map<string,vector<string>> adj_mp;
    unordered_map<string,int> mp;
    unordered_map<string,vector<string>> par;
    set<vector<string>> ans;
    vector<string> temp;

    void dfs(string w){
        if(w==""){
            ans.insert(temp);
            return;
        }
        for(auto v: par[w]){
            if(v!="")temp.push_back(v);
            dfs(v);
            if(v!="")temp.pop_back();
        }
    }

    void bfs(string begin, unordered_set<string> &st){
        queue<string> q;
        q.push(begin);
        mp[begin] = 0;
        par[begin].push_back("");
        while(!q.empty()){
            auto node = q.front();
            q.pop();
            for(auto v:adj_mp[node]){
                if(mp.find(v)==mp.end()){
                    mp[v] = mp[node]+1;
                    par[v].push_back(node);
                    q.push(v);
                }
                else if(mp[v] == mp[node]+1){
                    par[v].push_back(node);
                }
            }
        }
    }

    vector<vector<string>> findLadders(string beginWord, string endWord, vector<string>& wordList) {
        unordered_set<string> st;
        for(int i=0;i<wordList.size();i++){
            st.insert(wordList[i]);
        }
        st.insert(beginWord);
        for(auto s: st){
            for(int j=0;j<s.size();j++){
                char ch = s[j];
                for(int k=0;k<26;k++){
                    if('a'+k == ch) continue;
                    string tmp = s;
                    tmp[j]=('a'+k);
                    if(st.find(tmp)!=st.end()){
                        adj_mp[s].push_back(tmp);
                    }
                }
            }
        }
        bfs(beginWord, st);
        for(auto p:par){
            cout<<p.first<<":[";
            for(int i=0;i<p.second.size();i++){
                cout<<p.second[i]<<" ";
            }
            cout<<"]";
        }
        temp.push_back(endWord);
        dfs(endWord);
        vector<vector<string>> ans1;
        for(auto vs: ans){
            reverse(vs.begin(),vs.end());
            ans1.push_back(vs);
        }
        return ans1;
    }
};
17400