3sum.py

class Solution:
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        res = []
        nums.sort()
        
        if len(nums) < 3:
            return res
        
        for i in range(len(nums) - 2):
            
            if i > 0 and nums[i] == nums[i-1]: 
                continue
            
            l, r = i + 1, len(nums) - 1
            while l < r :
                s = nums[i] + nums[l] + nums[r]
                if s == 0:
                    res.append([nums[i] ,nums[l] ,nums[r]])
                    l += 1; r -= 1
                    while l < r and nums[l] == nums[l - 1]: l += 1
                    while l < r and nums[r] == nums[r + 1]: r -= 1
                elif s < 0 :
                    l += 1
                else:
                    r -= 1
        return res