1. Two Sum

 

1. Two Sum

Easy

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Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

 

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]

 

Constraints:

• 2 <= nums.length <= 105
• -109 <= nums[i] <= 109
• -109 <= target <= 109
• Only one valid answer exists.

 

 

class Solution:
  def twoSum(self, nums: List[int], target: int) -> List[int]:
    # number -> index
    map = {}
    for i, num in enumerate(nums):
      remain = target - num
      if remain in map:
        return [i, map[remain]]
      else:
        map[num] = i
        

 

知识点：

 

1 enumerate

2 hashmap