1. Two Sum

# O(n) time || O(n) space
def two_sum(self, nums: List[int], target: int) -> List[int]:
    dic = collections.defaultdict(int)
    for i, num in enumerate(nums):
        if target - num in dic:
            return [i, dic[target - num]]

        dic[num] = i

In this solution, we use a dictionary dic to store the numbers encountered so far along with their indices.
As we iterate through the array, we check if the complement (target - num) exists in the num_map dictionary.
If it does, we return the indices of the two numbers.
Otherwise, we add the current number and its index to the dictionary.