diff --git a/3-longest-substring-without-repeating-characters/3-longest-substring-without-repeating-characters.py b/3-longest-substring-without-repeating-characters/3-longest-substring-without-repeating-characters.py
new file mode 100644
index 0000000..df1d51b
--- /dev/null
+++ b/3-longest-substring-without-repeating-characters/3-longest-substring-without-repeating-characters.py
@@ -0,0 +1,26 @@
+class Solution(object):
+    def lengthOfLongestSubstring(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        letters = [x for x in s]
+        longestLength = 1
+        
+        if len(letters) == 0: return 0
+        
+        for i in range(len(letters)):
+            dictionary = {}
+            for j in range(i, len(letters)):
+                if dictionary.get(letters[j]) == None:
+                    dictionary[letters[j]] = 0
+                else:
+                    if j-i > longestLength:
+                        longestLength = j-i
+                    break
+                    
+                if j == len(letters) - 1:
+                    if j-i+1 > longestLength:
+                        longestLength = j-i+1
+                        return longestLength
+        return longestLength
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