Leetcode - 15. 3Sum

문제

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LeetCode

정답

오답

예상했지만, Brute force로 하면 TLE가 나온다.

class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        nums = sorted(nums)

        result = []
        for ii in range(len(nums)):
            if ii > 0 and nums[ii] == nums[ii - 1]:
                continue
            for jj in range(ii + 1, len(nums)):
                if jj > ii + 1 and nums[jj] == nums[jj - 1]:
                    continue
                for kk in range(jj + 1, len(nums)):
                    if kk > jj + 1 and nums[kk] == nums[kk - 1]:
                        continue
                    res = [nums[ii], nums[jj], nums[kk]]
                    if sum(res) == 0 and res not in result:
                        result.append(res)
                        break
        return result

쓰리 포인터 구현

가장 왼쪽 숫자를 left 로 놓고, 나머지 숫자 내에서 투 포인터로 합을 계산하는 방식이다.

class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        nums = sorted(nums)

        result = []
        for left in range(len(nums) - 2):
            if left > 0 and nums[left] == nums[left - 1]:
                continue

            mid = left + 1
            right = len(nums) - 1
            while mid < right:
                res = [nums[left], nums[mid], nums[right]]
                res_sum = sum(res)
                if res_sum < 0:
                    mid += 1
                elif res_sum == 0:
                    result.append(res)
                    while mid < right and nums[mid] == nums[mid + 1]:
                        mid += 1
                    while mid < right and nums[right] == nums[right - 1]:
                        right -= 1
                    mid += 1
                    right -= 1
                else:
                    right -= 1

        return result