Day13 - 18.四数之和

题目链接：https://leetcode.cn/problems/4sum/

核心方法：双指针

解析：比”Day12 - 15. 三数之和“多了一个移动的下标 j

class Solution:
    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
        nums.sort()
        n = len(nums)

        result = []

        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
                left,right = j+1,n-1
                while left < right:
                    s = nums[i] + nums[j] + nums[left] + nums[right]
                    if s == target:
                        result.append([nums[i],nums[j],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

                    elif s < target:
                        left += 1
                    else:
                        right -= 1
        return result