题目

题解

暴力法

class Solution:def fourSum(self, nums: List[int], target: int) -> List[List[int]]:if len(nums) < 4:return []nums.sort()N = len(nums)res = []for i in range(N-3):for j in range(i+1, N-2):for k in range(j+1, N-1):for m in range(k+1, N):tmp = [nums[i], nums[j], nums[k], nums[m]]if sum(tmp) == target and tmp not in res:res.append(tmp)return res

双指针

class Solution:def Nsum(self, nums: List[int], N, start, target):"""Params:nums: 输入列表n: 求几个数之和，n=2 两数之和， n=3三数之和start: 从列表的第几个元素开始搜索target: 之和要为多少""" nums.sort()res = []n = len(nums)# 至少是 2Sum，且数组大小不应该小于 nif n < 2 or n < N:return res# 2Sum 是 base caseif N == 2:lo, hi = start, n - 1while lo < hi:left, right = nums[lo], nums[hi]if left + right == target:res.append([left, right])# 左边相同的元素移动while lo < hi and nums[lo] == left:lo += 1# 左边相同的元素移动while lo < hi and nums[hi] == right:hi -= 1elif left + right > target:while lo < hi and nums[hi] == right:hi -= 1elif left + right < target:while lo < hi and nums[lo] == left:lo += 1# n > 2 时，递归计算 (n-1)Sum 的结果else:i = start# 遍历整个列表while i < n:left = nums[i]sub = self.Nsum(nums, N-1, i+1, target-nums[i])for item in sub:res.append([left] + item)while i < n and nums[i] == left:i += 1return resdef fourSum(self, nums: List[int], target: int) -> List[List[int]]:res = self.Nsum(nums, 4, 0, target)return res