Refactor : Two Sum

Author: printjin-gmailcom

two-sum/printjin-gmailcom

@@ -1,6 +1,8 @@
 class Solution:
     def twoSum(self, nums, target):
-        for i in range(len(nums)):
-            for j in range(i + 1, len(nums)):  
-                if nums[i] + nums[j] == target:
-                    return [i, j]
+        num_map = {}
+        for i, num in enumerate(nums):
+            left = target - num
+            if left in num_map:
+                return [num_map[left], i]
+            num_map[num] = i