0018leetcode算法实现之四数之和4sumpython&golang实现 Marathon

给你一个由 n 个整数组成的数组 nums ，和一个目标值 target 。请你找出并返回满足下述全部条件且不重复的四元组 [nums[a], nums[b], nums[c], nums[d]] （若两个四元组元素一一对应，则认为两个四元组重复）：

0 <= a, b, c, d < n
a、b、c 和 d 互不相同
nums[a] + nums[b] + nums[c] + nums[d] == target
你可以按 任意顺序 返回答案 。

示例 1：

输入：nums = [1,0,-1,0,-2,2], target = 0
输出：[[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
示例 2：

输入：nums = [2,2,2,2,2], target = 8
输出：[[2,2,2,2]]

提示：

1 <= nums.length <= 200
-109 <= nums[i] <= 109
-109 <= target <= 109

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/4sum

python

# 四数之和

class Solution:
    def fourSum(self, nums:[int], target: int) -> [int]:
        """
        排序加双指针，参考三数之和，时间O(n^3 + nlogn), 空间O(n)
        思路：

        算法流程：

        :param nums:
        :param target:
        :return:
        """
        res = []
        if not nums or len(nums) < 4:
            return res
        n = len(nums)
        nums.sort()
        for first in range(n-3):
            if first > 0 and nums[first] == nums[first-1]: # 检查重复
                continue
            for second in range(first+1, n-2):
                if second > first+1 and nums[second] == nums[second-1]: # 检查重复
                    continue
                left, right = second+1, n-1
                while left < right:
                    target_ = nums[first] + nums[second] - target
                    if target_ < -(nums[left] + nums[right]): # python不考虑溢出
                        left += 1
                    elif target_ > -(nums[left] + nums[right]):
                        right -= 1
                    else:
                        res.append([nums[first], nums[second], nums[left], nums[right]])
                        while left < right and nums[left+1]==nums[left]: # 检查重复
                            left += 1
                        while left < right and nums[right-1] == nums[right]: # 检查重复
                            right -= 1
                        left += 1
                        right -= 1
        return  res


if __name__ == "__main__":
    nums = [2,4,6,2,9,-12,43,5,-7,21,-20,4]
    nums1 = [2,2,2,2,2,2]
    test = Solution()
    print(test.fourSum(nums, 0))
    print(test.fourSum(nums1, 8))

glang

func fourSum(nums []int, target int) [][]int {
    res := [][]int{}
	if len(nums) < 4 {
		return res
	}
	n := len(nums)
	sort.Ints(nums)
	for first := 0; first < n-3; first++ {
		if first > 0 && nums[first] == nums[first-1] {
			continue
		}
		for second := first + 1; second < n-2; second++ {
			if second > first+1 && nums[second] == nums[second-1] {
				continue
			}
			left, right := second+1, n-1
			for left < right {
				if nums[first]+nums[second]-target < -(nums[left] + nums[right]) {
					left++
				} else if nums[first]+nums[second]-target > -(nums[left] + nums[right]) {
					right--
				} else {
					res = append(res, []int{nums[first], nums[second], nums[left], nums[right]})
					for left < right && nums[left+1] == nums[left] {
						left++
					}
					for left < right && nums[right-1] == nums[right] {
						right--
					}
					left++
					right--
				}
			}
		}
	}
	return res
}