<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 only1diff(string &u,string &v){
    if(u.size()!=v.size() || u==v) return false;
    if(u==v) return false;
    int cnt=0;
    for(int i=0;i<u.size();i++){
        if(u[i]!=v[i]) cnt++;
        if(cnt>=2) return false;
    }
    return true;
}
    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
        // grap 
        unordered_map<string,vector<string>>adj;
        int n=wordList.size();
        for(int j=0;j<n;j++){ 
                if(only1diff(beginWord,wordList[j])){
                    adj[beginWord].push_back(wordList[j]);
                     adj[wordList[j]].push_back(beginWord);
                }
          }
        for(int i=0;i<n;i++){
          string u=wordList[i];
        //   if(adj.find(u)!=adj.end()) continue; 
          for(int j=i+1;j<n;j++){ 
                if(only1diff(u,wordList[j])){
                    adj[u].push_back(wordList[j]);
                    adj[wordList[j]].push_back(u);
                }
          }
        }
        // if(adj.find(beginWord)==adj.end()) return 0;
        // grap view code
        unordered_map<string ,int > dis;
        for(auto node:adj){
            dis[node.first]=INT_MAX;
        }
        dis[beginWord]=0;
        priority_queue<pair<int,string>,vector<pair<int,string>>,greater<pair<int,string>>> pq;
        pq.push({0,beginWord});
        while(!pq.empty()){
            auto front=pq.top();pq.pop();
            string fnode=front.second;
            int fd=front.first;
            for(auto ch:adj[front.second]){
               if(fd+1<dis[ch]){
                dis[ch]=fd+1;
                pq.push({fd+1,ch});
               }
            }
        }
        if(dis[endWord]==0 || dis[endWord]==INT_MAX){
            return 0;
        }
        return dis[endWord]+1;
        // for(auto ch:adj){ cout<<ch.first<<" = ";
        //     for(auto e:ch.second){     cout<<e<<" ,"; } cout<<endl; 
        // }
        //SOLVE USING DFS
        // int len=1;
        // unordered_map<string,bool> vis;
        // int ans=INT_MAX;
        // dfs(beginWord,len,vis,adj,endWord,ans);
        // // cout<<" last me";
        // if(ans==INT_MAX) return 0;
        // return ans; 
    }
    void dfs(string src,int len,unordered_map<string,bool>vis, unordered_map<string,vector<string>>&adj,string &des,int &ans){
        // cout<<" call "<<src<<" len:"<<len<<endl;
        if(src==des){
            ans=min(ans,len);
            // cout<<" base "<<ans<<"|| ";
            return ;
        }
        vis[src]=true;
        for(auto ch:adj[src]){
            if(!vis[ch]){
                dfs(ch,len+1,vis,adj,des,ans);
            }
        }
    }
};
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