added solution to 136 Single Number

Author: Dominik Schauer

algorithms/136_Single_Number_hash_table.py

@@ -0,0 +1,11 @@
+from collections import defaultdict
+class Solution:
+    def singleNumber(self, nums: List[int]) -> int:
+        cnt_dict = defaultdict(int)
+        
+        for num in nums: 
+            cnt_dict[num] += 1
+            
+        for num in cnt_dict:
+            if cnt_dict[num] == 1:
+                return num

algorithms/136_Single_Number_set.py

@@ -0,0 +1,6 @@
+class Solution:
+    def singleNumber(self, nums: List[int]) -> int:
+        nums_sum = sum(nums)
+        set_sum = sum(set(nums))
+        
+        return 2*set_sum - nums_sum