added solutions to class Solution:

Author: Dominik Schauer

algorithms/268_Missing_Number_set.py

@@ -0,0 +1,3 @@
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+        return tuple(set(range(len(nums)+1)) - set(nums))[0]

algorithms/268_Missing_Number_sort.py

@@ -0,0 +1,10 @@
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+                    
+        nums.sort()
+        
+        for i in range(len(nums)):
+            if(nums[i] != i):
+                return i
+        
+        return len(nums)