<p>Given a string <code>s</code> and an integer <code>k</code>, return <em>the length of the longest substring of</em> <code>s</code> <em>such that the frequency of each character in this substring is greater than or equal to</em> <code>k</code>.</p>

<p data-pm-slice="1 1 []">if no such substring exists, return 0.</p>

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

<pre>
<strong>Input:</strong> s = &quot;aaabb&quot;, k = 3
<strong>Output:</strong> 3
<strong>Explanation:</strong> The longest substring is &quot;aaa&quot;, as &#39;a&#39; is repeated 3 times.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;ababbc&quot;, k = 2
<strong>Output:</strong> 5
<strong>Explanation:</strong> The longest substring is &quot;ababb&quot;, as &#39;a&#39; is repeated 2 times and &#39;b&#39; is repeated 3 times.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
	<li><code>1 &lt;= k &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    bool helper(string str,int size,int k){
         unordered_map<char,int>mp;
         for(int i =0;i<size;i++){
            mp[str[i]]++;
         }
         bool flag = true;
         for(auto x : mp){
             if(x.second<k){
                flag = false;
             }
         }
         if(flag){
            return true;
         }
         int i = 0;
         for(int j =size;j<str.size();j++){
              mp[str[j]]++;
              mp[str[i]]--;
              if(mp[str[i]]==0){
                 mp.erase(str[i]);
              }
              i++;
                        flag = true;
                        for(auto x : mp){
                            if(x.second<k){
                                flag = false;
                            }
                        }
                        if(flag){
                            return true;
                        }

         }
         return false;
    }
    int longestSubstring(string s, int k) {
        int n = s.length();
        int start = k;
        int end = n;
        int ans = 0;
        // while(start<=end){
        //      int mid = (start+end)/2;
        //      if(helper(s,mid,k)){
        //          start = mid+1;
        //          ans = max(ans,mid);
        //      }else{
        //          end = mid-1;
        //      }
        // }
        for(int mid = k;mid<=s.size();mid+=1){
             if(helper(s,mid,k)){
                 ans = mid;
             }
        }
        return ans;
    }
};
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