Create 268-Missing-Number.py

Author: neetcode-gh

268-Missing-Number.py

@@ -0,0 +1,7 @@
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+        res = len(nums)
+        
+        for i in range(len(nums)):
+            res += (i - nums[i])
+        return res