[LeetCode]15 三数之和

题目描述

给定一个包含 n 个整数的数组 nums，判断 nums 中是否存在三个元素 a，b，c ，使得 a + b + c = 0 ？找出所有满足条件且不重复的三元组。

注意：答案中不可以包含重复的三元组。

例如, 给定数组 nums = [-1, 0, 1, 2, -1, -4]，
满足要求的三元组集合为：
[
  [-1, 0, 1],
  [-1, -1, 2]
]

代码

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class Solution:
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        dict = {}
        for ele in nums:
            if ele not in dict:
                dict[ele] = 0
            dict[ele] += 1
            
        if 0 in dict and dict[0] > 2:
            result = [[0,0,0]]
        else:
            result = []
        
        pos = [p for p in dict if p > 0]
        neg = [n for n in dict if n < 0]
        
        for p in pos:
            for n in neg:
                target = -(p + n)
                if target in dict:
                    if target == p and dict[p] > 1:
                        result.append([n, p, p])
                    elif target == n and dict[n] > 1:
                        result.append([n, n, p])
                    elif target < n or target > p or target == 0:
                        result.append([n, target, p])
        return result