1. Two Sum

Question: Two Sum
Solution

1. 將出現過的數字存在 dictionary 中，key 為數字，value 為 index
2. 找 pair 時直接去 dictionary 找即可

from collections import defaultdict

class Solution:

def twoSum(self, nums: List[int], target: int) -> List[int]:

num_map = defaultdict(int)

for index, num in enumerate(nums):

if target - num in num_map:

return [num_map[target-num], index]

num_map[num] = index

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