leetcode(3)

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of z

class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        #三個數字
        if len(nums) <3:
            return []
        len1 = len(nums)-1
        nums = sorted(nums)
        l1 = []
        for i in range(len1-1):
            if i > 0 and nums[i] == nums[i-1]: continue
            left = i+1
            right = len1
            if nums[i] > 0:
                break
            while left<right:
                checked = nums[i] + nums[right] + nums[left]
                 if checked == 0:
                    l1.append([nums[i],nums[left],nums[right]])
                    left+=1
                    right-=1
                    while left<right and nums[left] == nums[left-1] : left+=1
                    while left<right and nums[right] == nums[right+1]: right-=1
                elif checked <0:
                    left+=1
                else:
                    right-=1
        return l1