<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>the <strong>number of words</strong> in the <strong>shortest transformation sequence</strong> from</em> <code>beginWord</code> <em>to</em> <code>endWord</code><em>, or </em><code>0</code><em> if no such sequence exists.</em></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> 5
<strong>Explanation:</strong> One shortest transformation sequence is &quot;hit&quot; -&gt; &quot;hot&quot; -&gt; &quot;dot&quot; -&gt; &quot;dog&quot; -&gt; cog&quot;, which is 5 words long.
</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> 0
<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;= 10</code></li>
	<li><code>endWord.length == beginWord.length</code></li>
	<li><code>1 &lt;= wordList.length &lt;= 5000</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>
</ul>

class Solution {
    private:
    int fun(unordered_map<string,vector<string>>mp,string src, string target){
        priority_queue<pair<int,string>,vector<pair<int,string>>,greater<pair<int,string>>>pq;
        pq.push({1,src});
        unordered_set<string>s;
        s.insert(src);
        while(!pq.empty()){
           int cnt=pq.top().first;
           string node=pq.top().second;
           pq.pop();
           for(int i=0;i<mp[node].size();i++){
            if(mp[node][i]==target) return cnt+1;
            if(s.find(mp[node][i])==s.end()){
              s.insert(mp[node][i]);
            pq.push({cnt+1,mp[node][i]});
            }
           }
        }
        return 0;
    }
public:
    int ladderLength(string beginword, string endword, vector<string>& wordlist) {
    
      unordered_map<string,vector<string>>mp;
      int n=wordlist.size();
      int cnt=0;
      unordered_set<string>s;
      for(int i=0;i<n;i++){
       s.insert(wordlist[i]);
      }
      for(int k=0;k<beginword.size();k++){
            char temp=beginword[k];
            string tempstr=beginword;
          for(int j=0;j<26;j++){
             char ch='a'+j;
             if(temp==ch)continue;
             beginword[k]=ch;
             if(s.find(beginword)!=s.end())mp[tempstr].push_back(beginword);
          }
          beginword[k]=temp;
        }
      for(int i=0;i<n;i++){
        for(int k=0;k<wordlist[i].size();k++){
            char temp=wordlist[i][k];
            string tempstr=wordlist[i];
          for(int j=0;j<26;j++){
             char ch='a'+j;
             if(temp==ch)continue;
             wordlist[i][k]=ch;
             if(s.find(wordlist[i])!=s.end())mp[tempstr].push_back(wordlist[i]);
          }
          wordlist[i][k]=temp;
        }
      }
       
        if(s.find(endword)==s.end() || mp[beginword].size()==0) return 0;
       return fun(mp,beginword,endword);



    }
};
50575