4. 4SumLeet.py

class Solution:
    def fourSum(self, nums: [int], target: int) -> [[int]]:
        nums.sort()
        n = len(nums)
        ans = []
        for i in range(n):
            if i > 0 and nums[i] == nums[i-1]: 
                continue
            for j in range(i+1, n):
                if j != i+1 and nums[j] == nums[j-1]:
                    continue
                k = j+1
                l = n-1
                while k<l:
                    s = nums[i]
                    s += nums[j]
                    s += nums[k]
                    s += nums[l]
                    if s == target:
                        ans.append([nums[i], nums[j], nums[k], nums[l]])
                        l -= 1
                        k += 1
                        while (k<l and nums[k] == nums[k-1]):
                            k+=1
                        while (k<l and nums[l] == nums[l+1]):
                            l-=1
                    elif s > target:
                        l-=1
                    else:
                        k+=1
        return ans
    
# Link: https://leetcode.com/problems/4sum/