15. 3Sum(세 수의 합)

class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        results = []
        nums.sort()
        
        for i in range(len(nums) - 2):
            #중복된 값 건너뛰기
            if i > 0 and nums[i] == nums[i - 1]:
                continue
            
            #값을 좁혀가며 합 계산
            left, right = i + 1, len(nums) - 1
            while left < right:
                sum = nums[i] + nums[left] + nums[right]
                if sum > 0:
                    right -= 1
                elif sum < 0:
                    left += 1
                else:
                    results.append([nums[i], nums[left], nums[right]])
                    while left < right and nums[left] == nums[left + 1]:
                        left += 1
                    while left < right and nums[right] == nums[right - 1]:
                        right -= 1
                    left += 1
                    right -= 1
        return results