diff --git a/a.cpp b/a.cpp
new file mode 100644
index 0000000..0745595
--- /dev/null
+++ b/a.cpp
@@ -0,0 +1,63 @@
+
+#include <bits/stdc++.h> 
+  
+using namespace std; 
+  
+string LongestSubstring(string str) 
+{ 
+    int i; 
+    int n = str.length(); 
+  
+ 
+    int st = 0; 
+    int currlen; 
+  
+    int maxlen = 0; 
+  
+ 
+    int start; 
+    unordered_map<char, int> pos; 
+    pos[str[0]] = 0; 
+  
+    for (i = 1; i < n; i++) { 
+  
+    
+        if (pos.find(str[i]) == pos.end()) 
+            pos[str[i]] = i; 
+  
+        else { 
+           
+            if (pos[str[i]] >= st) { 
+  
+                currlen = i - st; 
+                if (maxlen < currlen) { 
+                    maxlen = currlen; 
+                    start = st; 
+                } 
+  
+             
+                st = pos[str[i]] + 1; 
+            } 
+  
+            
+            pos[str[i]] = i; 
+        } 
+    } 
+  
+  
+    if (maxlen < i - st) { 
+        maxlen = i - st; 
+        start = st; 
+    } 
+  
+    
+    return str.substr(start, maxlen); 
+} 
+  
+int main() 
+{ 
+    string str = "somiljain"; 
+    cout <<LongestSubstring(str); 
+    return 0; 
+} 
+