[LeetCode] 1번 Two Sum

문제

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.

예제

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]

조건

Constraints:

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

답

풀이 1

브루트 포스를 활용한 풀이

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        for i in range(len(nums)):
            for j in range(i+1, len(nums)):
                if nums[i]+nums[j] == target:
                	x = [i,j]
                    return(x)

풀이 2

in을 이용한 풀이

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        for i, n in enumerate(nums):
            complement = target - n
            
            if complement in nums[i + 1:]:
                return [nums.index(n), nums[i + 1:].index(complement) + (i + 1)]

풀이 3

첫 번째 수를 뺀 결과 키 조회

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        nums_map = {}
        
        for i, num in enumerate(nums):
            nums_map[num] = i
        
        for i, num in enumerate(nums):
            if target - num in nums_map and i != nums_map[target - num]:
                return [i, nums_map[target - num]]

풀이 4

조회 구조 개선

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