<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:
    vector<string> newstring(string s,string &s2){

        int i=0;
        while(s[i]==s2[i]) i++;
        vector<string>ans;

        for(int ind=i;ind<s.size();ind++){
            if(s[ind] == s2[i]){
                swap(s[ind],s[i]);
                ans.push_back(s);
                swap(s[ind],s[i]);
            }
        }

        return ans;
    }
    
    int kSimilarity(string s1, string s2) {
        if(s1==s2) return 0;
        set<string>st;
        queue<string>q;

        st.insert(s1);
        q.push(s1);
        
        int level=0;
        while(q.size()){
            int sz=q.size();
            while(sz--){
                string s=q.front();
                q.pop();

                vector<string>words=newstring(s,s2);
                for(auto &it:words){
                    if(it==s2) return level+1;
                    if(st.count(it)==0) {
                        st.insert(it);
                        q.push(it);
                    }
                }
            }
            level++;
        }

        return 0;
    }
};
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