<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>

struct node{
    string s;
    vector<node*> nbr;
    node(string k) : s(k) {} 
};
class Solution {
public:
    bool valid(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 bfs(string s, unordered_map<string, node*> &mp, string e){
        if(mp.find(s) == mp.end()) return INT_MAX;
        unordered_map<string, bool> vis;
        for(auto it = mp.begin() ; it != mp.end() ; it++){
            vis[it->first] = 0;
        }
        queue<pair<node*,int>> qp;
        qp.push({mp[s], 2});
        vis[s] = 1;
        while(!qp.empty()){
            auto x = qp.front();
            qp.pop();
            node* n = x.first;
            int level = x.second;
            if(n->s == e) return level;
            for(auto nbr : n->nbr){
                if(vis[nbr->s]) continue;
                qp.push({nbr, level + 1});
                vis[nbr->s] = 1;
            }
        }
        return INT_MAX;
    }
    
    
    
    int ladderLength(string b, string e, vector<string>& wordList) {
        unordered_map<string, node*> mp;
        
        for(auto i : wordList){
            if(mp.find(i) == mp.end()){
                mp[i] = new node(i);
            }
        }
        
        for(int i = 0 ; i< wordList.size() ; i++){
            for(int j = i + 1 ; j<wordList.size() ; j++){
                if(valid(wordList[i], wordList[j])){
                    mp[wordList[i]]->nbr.push_back(mp[wordList[j]]);
                    mp[wordList[j]]->nbr.push_back(mp[wordList[i]]);                    
                }
            }
        }
        

            
    int ans = INT_MAX;
                   
    for(auto i : wordList){
        if(valid(i, b)){
            ans = min(ans, bfs(i, mp, e));
        }
    }
    ans =  ans == INT_MAX ? 0 : ans;
                   
    return ans;
                   
                        
                   }
    
};
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