<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 {
    bool check(unordered_map<char,int> freq, int k) {
        for (auto p:freq){
            if (p.second<k)
                return false;
        }
        return true;
    }
public:
    int longestSubstring(string s, int k) {
        int n=s.length();
        unordered_set<char> uq;
        for(auto x:s) {
            uq.insert(x);
        }
        int totalUq = uq.size();
        int ans=0;
        for(int tu=1;tu<=totalUq;tu++) {
            unordered_map<char, int> freq;
            int i=0,j=0;
            while(j<n){
                freq[s[j]]++;

                while(freq.size()>tu) {
                    freq[s[i]]--;
                    if (freq[s[i]]==0)
                        freq.erase(s[i]);

                    i++;
                }
                if (check(freq, k)) {
                    ans = max(ans, j-i+1);
                }
                j++;
            }
        }

        return ans;
    }
};
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