Create longest_substr_with_k_distinct_chars.cpp

Author: avidLearnerInProgress

longest_substr_with_k_distinct_chars.cpp

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+#include<bits/stdc++.h>
+using namespace std;
+
+int mod=1e9+7;
+#define F(a,b,var) for(int var=a;var<b;var++)
+#define FAST_INP  ios_base::sync_with_stdio(false);cin.tie(NULL)
+
+int longestKUniqueCharSubstr(string &s, int k) {
+    if(s.size() == 0) return 0;
+    if(k == 0  or k > s.size()) return -1;
+    
+    const int CHAR_RANGE = 128;
+    int frequency[CHAR_RANGE] = {0};
+    unordered_set<char> window; // sliding window -- at any instance, there has to be k characters in the window
+    int n = s.length();
+    int low, high; // low ... high -- keep track of window boundaries
+    int begin = 0, end = 0;
+    
+    for(low = 0, high = 0; high < n; high++) {
+        window.insert(s[high]);
+        frequency[s[high]]++;
+        
+        
+        while(window.size() > k) { //if the window exceeds k characters -- 
+            --frequency[s[low]]; //remove char from left
+            if(frequency[s[low]] == 0) { //if the character frequency becomes 0, it means the character is no more present in the window; so erase it
+                window.erase(s[low]);
+            }
+            low++; //increment left boundary 
+        }
+        
+        if(high - low > end - begin) { //store the ax
+            end = high, begin = low;
+        }
+    }
+    return end - begin + 1;
+}
+
+
+int main()
+ {
+	//code
+	
+        FAST_INP;
+        int T;
+        cin>>T;
+        while(T--)
+        {
+            int k;
+            string s;
+            
+            cin>>s>>k;
+            cout<<longestKUniqueCharSubstr(s, k)<<"\n";
+            
+        }
+	return 0;
+}