<p>Strings <code>s1</code> and <code>s2</code> are <code>k</code><strong>-similar</strong> (for some non-negative integer <code>k</code>) if we can swap the positions of two letters in <code>s1</code> exactly <code>k</code> times so that the resulting string equals <code>s2</code>.</p>

<p>Given two anagrams <code>s1</code> and <code>s2</code>, return the smallest <code>k</code> for which <code>s1</code> and <code>s2</code> are <code>k</code><strong>-similar</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s1 = &quot;ab&quot;, s2 = &quot;ba&quot;
<strong>Output:</strong> 1
<strong>Explanation:</strong> The two string are 1-similar because we can use one swap to change s1 to s2: &quot;ab&quot; --&gt; &quot;ba&quot;.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s1 = &quot;abc&quot;, s2 = &quot;bca&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> The two strings are 2-similar because we can use two swaps to change s1 to s2: &quot;abc&quot; --&gt; &quot;bac&quot; --&gt; &quot;bca&quot;.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s1.length &lt;= 20</code></li>
	<li><code>s2.length == s1.length</code></li>
	<li><code>s1</code> and <code>s2</code> contain only lowercase letters from the set <code>{&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;, &#39;e&#39;, &#39;f&#39;}</code>.</li>
	<li><code>s2</code> is an anagram of <code>s1</code>.</li>
</ul>

class Solution {
public:
    
    void Swap(string& k,int a,int b){
        char temp=k[a];
        k[a]=k[b];
        k[b]=temp;
    }
    int kSimilarity(string s1, string s2) {
        // unordered_map<char,vector<int>> Map;
        // for(int i=0;i<s1.length();i++){
        //     if(s1[i]!=s2[i]){
        //         Map[s1[i]].push_back(i);
        //     }
        // }
        // unordered_map<char,vector<int>> Map;
        if(s1==s2){
            return 0;
        }
        int idx,swap;
        string curr;
        unordered_set<string> Visited;
        vector<pair<string,pair<int,int>>> Queue;
        Visited.insert(s1);
        Queue.push_back(make_pair(s1,make_pair(0,0)));
        while(!Queue.empty()){
            auto t=Queue[0];
            curr=t.first;
            idx=t.second.first;
            swap=t.second.second;
            Queue.erase(Queue.begin());
            while(s2[idx]==curr[idx]){
                idx++;
            }
            for(int i=idx+1;i<s1.size();i++){
                if(curr[i]==s2[idx]){
                    Swap(curr,i,idx);
                    if(curr==s2){
                        return swap+1;
                    }
                    if(!Visited.count(curr)){
                        Queue.push_back(make_pair(curr,make_pair(idx+1,swap+1)));
                        Visited.insert(curr);
                    }
                    Swap(curr,i,idx);
                }
            }
        }
        return swap;
    }
};
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