Longest substring without duplicate

Author: Partho Biswas

README.md

@@ -21,7 +21,7 @@
   Can take a look into my <a href="https://leetcode.com/parthobiswas007/">leetcode profile</a> if interested. 
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algoexpert.io/python/Longest_Substring_Without_Duplication.py

@@ -0,0 +1,16 @@
+
+# O(n) time  |  O(min(n, a))  space
+def longestSubstringWithoutDuplication(string):
+    lastSeen = {}
+    longest = [0, 1] # Here 0 and 1 is the values in the 0 and 1 index. This variable stores the start and end index of of the longest string.
+    startIndex = 0
+    for i, char in enumerate(string):
+        if char in lastSeen:
+            startIndex = max(startIndex, lastSeen[char] + 1)
+        if longest[1] - longest[0] < i + 1 - startIndex: # Here 0 and 1 is the index of the value of longest array
+            longest = [startIndex, i + 1]
+        lastSeen[char] = i
+    return string[longest[0]:longest[1]]
+
+
+