diff --git a/CPP/Sliding window/longest-substring-without-repeating-characters.cpp b/CPP/Sliding window/longest-substring-without-repeating-characters.cpp
new file mode 100644
index 0000000..cccd3c9
--- /dev/null
+++ b/CPP/Sliding window/longest-substring-without-repeating-characters.cpp	
@@ -0,0 +1,30 @@
+// Problem: Longest Substring Without Repeating Characters
+#include <bits/stdc++.h>
+using namespace std;
+class Solution {
+  public:
+    int lengthofLongestSubstring(string s) {
+      vector < int > mpp(256, -1);
+
+      int left = 0, right = 0;
+      int n = s.size();
+      int len = 0;
+      while (right < n) {
+        if (mpp[s[right]] != -1)
+          left = max(mpp[s[right]] + 1, left);
+
+        mpp[s[right]] = right;
+
+        len = max(len, right - left + 1);
+        right++;
+      }
+      return len;
+    }
+};
+
+int main() {
+  string str = "takeUforward";
+  Solution obj;
+  cout << "The length of the longest substring without repeating characters is " << obj.lengthofLongestSubstring(str);
+  return 0;
+}
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