Added solution - LeetHub

Longest K unique characters substring - GFG/longest-k-unique-characters-substring.cpp

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+//{ Driver Code Starts
+//Initial template for C++
+
+#include <bits/stdc++.h>
+using namespace std;
+
+// } Driver Code Ends
+//User function template for C++
+
+class Solution{
+  public:
+    int longestKSubstr(string s, int k) {
+    // your code here
+    unordered_map<char,int>mp;
+    int n=s.size();
+    int start=0,end=0,ans=-1;
+    for(end=0;end<n;end++){
+        mp[s[end]]++;
+        if(mp.size()>k){
+            while(start<=end and start<n and mp.size()>k){
+                mp[s[start]]--;
+                if(mp[s[start]]==0){
+                    mp.erase(s[start]);
+                }
+                start++;
+            }
+        }
+        if(mp.size()==k){
+            ans=max(ans,end-start+1);
+        }
+    }
+    return ans;
+    }
+};
+
+//{ Driver Code Starts.
+int main() {
+    int t;
+    cin >> t;
+    while (t--) {
+        string s;
+        cin >> s;
+        int k;
+        cin >> k;
+        Solution ob;
+        cout << ob.longestKSubstr(s, k) << endl;
+    }
+}
+
+// } Driver Code Ends