Added Python solution to 128_Longest Consecutive Sequence (#140)

Author: JoyKrishan

Algorithms/Medium/128_LongestConsecutiveSequence/Solution.py

@@ -0,0 +1,15 @@
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        nums_set = set(nums)
+        longest = 0
+
+        for num in nums:
+            length = 0
+
+            if (num - 1) not in nums_set: 
+                while (num + length) in nums_set:
+                    length += 1
+            
+            longest = max(longest, length)
+        
+        return longest