add solution: two-sum

Author: dusunax

two-sum/dusunax.py

@@ -0,0 +1,33 @@
+'''
+# 1. Two Sum
+
+use a hash map to store the numbers and their indices.
+iterate through the list and check if the complement of the current number (target - nums[i]) is in the hash map.
+
+(assume that each input would have exactly one solution)
+- if it is a pairNum, return the indices of the two numbers.
+- if it is not, add the current number and its index to the hash map.
+
+
+## Time and Space Complexity
+
+```
+TC: O(n)
+SC: O(n)
+```
+
+#### TC is O(n):
+- iterating through the list just once to find the two numbers. = O(n)
+
+#### SC is O(n):
+- using a hash map to store the numbers and their indices. = O(n)
+'''
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        map = {}
+        for i in range(len(nums)):
+            pairNum = target - nums[i]
+            if pairNum in map:
+                return [map.get(pairNum), i]
+            map[nums[i]] = i