Leetcode - Two Sum - Solution

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 <= 103
• -109 <= nums[i] <= 109
• -109 <= target <= 109
• Only one valid answer exists.

Solution in Python

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