<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>

typedef pair<int, string> pis;

class Solution {
public:
    int word_diff(const string& word_1, const string& word_2) {
        int n = word_1.size();
        int diff = 0;
        for (int i = 0; i < n; i++) {
            if (word_1[i] != word_2[i]) diff++;
        }
        return diff;
    }

    int ladderLength(string begin_word, string end_word, vector<string>& word_list) {
        unordered_map<string, vector<string>> children;
        children[begin_word] = {};
        for (const string& word : word_list) {
            children[word] = {};
            for (const auto& p : children) {
                const string& prev_word = p.first;
                if (word_diff(prev_word, word) == 1) {
                    children[word].push_back(prev_word);
                    children[prev_word].push_back(word);
                }
            }
        }

        for (auto p : children) {
            cout << p.first << ": ";
            for (auto el : p.second) {
                cout << el << " ";
            }
            cout << endl;
        }

        if (children[end_word].size() == 0) return 0; // If end_word not connected to anything or not present return 0.

        unordered_map<string, int> distance;
        for (const auto& p : children) {
            distance[p.first] = INT_MAX;
        }

        priority_queue<pis, vector<pis>, greater<pis>> q;
        unordered_map<string, bool> visited;
        distance[begin_word] = 1;
        q.push({1, begin_word});

        while (!q.empty()) {
            const string word = q.top().second;
            q.pop();
            if (visited[word]) continue;
            visited[word] = true;

            for (const string& neighbor : children[word]) {
                if (distance[word] + 1 < distance[neighbor]) {
                    distance[neighbor] = distance[word] + 1;
                    q.push({distance[neighbor], neighbor});
                }
            }
        }

        return distance[end_word] == INT_MAX ? 0 : distance[end_word];
        /*
        unordered_map<string, bool> processed;
        min_queue.push({0, begin_word});
        distance[begin_word] = 0;
        while (!min_queue.empty()) {
            const string& word = min_queue.top().second;
            min_queue.pop();

            if (processed[word]) continue;
            processed[word] = true;

            for (const string& neighbor : children[word]) {
                if (distance[word] + 1 < distance[neighbor]) {
                    distance[neighbor] = distance[word] + 1;
                    min_queue.push({distance[neighbor] + 1, neighbor});
                }
            }
        }

        return distance[end_word] == INT_MAX ? 0 : distance[end_word];
        */
    }
};
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