LC18 四数之和

目录

• 1 题目
• 2 解答

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1 题目

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

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2 解答

# leetcode submit region begin(Prohibit modification and deletion)
class Solution:
    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
        nums.sort()
        n = len(nums)
        res = []
        for i in range(0 , n-3 , 1):

            if i >0 and nums[i-1]==nums[i]:
                continue

            if nums[i] + nums[i+1] + nums[i+2] + nums[i+3] > target:
                break


            if nums[i] + nums[n-3] + nums[-2] + nums[-1] < target:
                continue

            for j in range(i+1 , n-2 , 1):

                if j>i+1 and nums[j] == nums[j-1]:
                    continue

                if nums[i] + nums[j] + nums[j+1] + nums[j+2] > target:
                    break

                if nums[i] + nums[j] + nums[-1] + nums[-2] < target:
                    continue

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

                        left += 1
                        while (left < right and nums[left] == nums[left - 1]):
                            left += 1

                        right -= 1
                        while (left < right and nums[right] == nums[right + 1]):
                            right -= 1

                    elif s>target:
                        right -= 1
                    else:
                        left += 1
        return  res
# leetcode submit region end(Prohibit modification and deletion)