added daily challenge

Author: Pasindu-Vishmika

268. Missing Number.py

@@ -0,0 +1,8 @@
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+        n = len (nums)
+        for i in range (n+1):
+            if i in nums:
+                continue
+            else:
+                return i