Add a solution to two-sum problem.

Author: KyrieJ95

two-sum/joon.py

@@ -0,0 +1,28 @@
+from typing import List
+from typing import Dict
+
+
+class Solution:
+    # Time: O(n)
+    # Space: O(n)
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        # 1. Make a map {target - num : index of num} with the list nums.
+        # Time: O(n)
+        # Space: O(n)
+        mapOfSubtractedValueToIndex: Dict[int, int] = ({
+            target - num: index for index, num in enumerate(nums)
+        })
+        
+        # 2. ForEach num in nums, get value from the map.
+        # Time: O(n)
+        # Space: O(n)
+        result: List[int] = None
+        for indexOfNum, num in enumerate(nums):
+            try:
+                indexOfSubtractedValue = mapOfSubtractedValueToIndex[num]
+                if indexOfSubtractedValue == indexOfNum:
+                    continue
+                # 3. Return the index of num in nums and the value from the map.
+                return [indexOfNum, indexOfSubtractedValue]
+            except KeyError: 
+                continue