diff --git a/string_problems/longest_k_distinct.cpp b/string_problems/longest_k_distinct.cpp
new file mode 100644
index 0000000..acd6481
--- /dev/null
+++ b/string_problems/longest_k_distinct.cpp
@@ -0,0 +1,36 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int longestKDistinct(string s, int k) {
+    unordered_map<char, int> count;
+    int left = 0, maxLen = 0;
+
+    for (int right = 0; right < s.size(); right++) {
+        count[s[right]]++;
+
+        while (count.size() > k) {
+            count[s[left]]--;
+            if (count[s[left]] == 0)
+                count.erase(s[left]);
+            left++;
+        }
+
+        if (count.size() == k)
+            maxLen = max(maxLen, right - left + 1);
+    }
+
+    return maxLen;
+}
+
+int main() {
+    string s;
+    int k;
+    cout << "Enter string: ";
+    cin >> s;
+    cout << "Enter K: ";
+    cin >> k;
+
+    int result = longestKDistinct(s, k);
+    cout << "Length of longest substring with " << k << " distinct characters is: " << result << endl;
+    return 0;
+}