2_pointers.py

1. FourSum:
You are given an integer array nums of size n, return an array of all the unique quadruplets 
[nums[a], nums[b], nums[c], nums[d]] such that:

0 <= a, b, c, d < n
a, b, c, and d are distinct.
nums[a] + nums[b] + nums[c] + nums[d] == target
You may return the answer in any order. Note: [1,0,3,2] and [3,0,1,2] are considered as same quadruplets.
Example 1:
Input: nums = [3,2,3,-3,1,0], target = 3
Output: [[-3,0,3,3],[-3,1,2,3]]

# Solution
def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
    nums.sort()
    result = []

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

        for j in range(i + 1, len(nums)):
            if j > i + 1 and nums[j] == nums[j-1]:
                continue 

            l = j + 1 
            r = len(nums) - 1 

            while(l < r):
                array = [nums[i], nums[j], nums[l], nums[r]]
                if sum(array) == target:
                    result.append(array)
                    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 sum(array) < target:
                    l += 1 
                else:
                    r -= 1 
    return result