1. Two Sum

Python

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        m = {}
        for i in range(len(nums)):
            c = target - nums[i]
            if c in m:
                return [m[c], i]
            m[nums[i]] = i

• T: $O(N)$
• S: $O(N)$