diff --git a/test008.cpp b/test008.cpp
new file mode 100644
index 0000000..88e7aa9
--- /dev/null
+++ b/test008.cpp
@@ -0,0 +1,17 @@
+class Solution {
+public:
+    int lengthOfLongestSubstring(string s) {
+        int n = s.length();
+        int ret = 0;
+        unordered_map<char, int> count;
+        int l = 0;
+        for(int r = 0; r < n; r++){
+            count[s[r]]++;
+            while(count[s[r]] >= 2){
+                count[s[l++]]--;
+            }
+            ret = max(ret, r - l + 1);
+        }
+        return ret;
+    }
+};
\ No newline at end of file