3Sum.py

# 15. 3Sum
# Medium

# 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 zero.

# Note:

# The solution set must not contain duplicate triplets.

# Example:

# Given array nums = [-1, 0, 1, 2, -1, -4],

# A solution set is:
# [
#   [-1, 0, 1],
#   [-1, -1, 2]
# ]
'''
More Edge Cases : 
[0,0,0], 4 0's
'''

class Solution(object):
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        nums.sort()
        index = []
        
        for i in range(len(nums)-2):
            
            if i != 0 and nums[i] == nums[i-1]:
                continue
                
            left, right = i+1,len(nums)-1
            
            while left < right:
                
                sum = nums[i] + nums[left] + nums[right]
                
                #print(nums[i],nums[left],nums[right],sum)
                
                if(sum > 0):
                    right -= 1
                elif(sum < 0):
                    left += 1
                if(sum == 0):
                    index.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 index