Add solution for Two Sum

Author: jamiebase

two-sum/gcount85.py

@@ -0,0 +1,19 @@
+"""
+- Approach:
+  Make a dictionary.
+  The key is difference from target and the value is its index,
+  then iterate the number array and with its value, find the key in the dictionary.
+- Time Complexity: O(2N) => O(N)
+- Space complexity: O(N)
+"""
+
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        num_dic = {}
+        for i, v in enumerate(nums):  # O(N)
+            num_dic[target - v] = i
+
+        for i, v in enumerate(nums):  # O(N)
+            if v in num_dic and num_dic[v] != i:
+                return [num_dic[v], i]