两数之和

建立对应的哈希表，key=数，value=索引，遍历一次，每次找target-num即可：

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        
        temp = {}
        
        for i, num in enumerate(nums):
            try:
                index = temp[target-num]
                return [index, i]
            except:
                temp[num] = i