<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 {
public:
    bool compare(string a,string b){
        int cnt=0;
        for(int i=0;i<a.size();i++) if(a[i]!=b[i]) cnt++;
        return cnt<=1;
    }
    int shortest(int start,int end,vector<int> adj[],int n){
        vector<int> dist(n+1,1e9);
        vector<bool> vis(n+1,false);
        priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>> pq;
        pq.push({1,start});
        dist[start]=0;
        while(!pq.empty()){
            auto top= pq.top();
            vis[top.second]=1;
            pq.pop();
            for(auto it: adj[top.second]){
                if(!vis[it] && dist[it]>top.first+1){
                    dist[it]= top.first+1;
                    pq.push({dist[it],it});
                }
            }
        }
        // for(auto it: dist) cout<<it<<' ';
        return dist[end]==1e9?0:dist[end];
    }
    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
        bool ans=0;
        for(auto it: wordList) if(it==endWord) ans=1;
        if(ans==0) return 0;
        set<string> s;
        for(auto it: wordList) s.insert(it);
        s.insert(beginWord);
        vector<string> arr;
        for(auto it:s) arr.emplace_back(it);
        int n= arr.size();
        vector<int> adj[n+1];
        for(int i=1;i<n;i++){
            for(int j=i-1;j>=0;j--){
                if(!compare(arr[i],arr[j])) continue;
                else{
                    adj[i].emplace_back(j);
                    adj[j].emplace_back(i);
                }
            }
        }
        int start,end;
        for(int i=0;i<n;i++){
            if(arr[i]==beginWord) start=i;
            else if(arr[i]==endWord) end=i;
        }
        return shortest(start,end,adj,n);
    }
};
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