给出一个有n个整数的数组S，在S中找到三个整数a, b, c，找到所有使得a + b + c = 0的三元组。
在三元组(a, b, c)，要求a <= b <= c。
结果不能包含重复的三元组。
您在真实的面试中是否遇到过这个题？ 是
样例
如S = {-1 0 1 2 -1 -4}, 你需要返回的三元组集合的是：
(-1, 0, 1)
(-1, -1, 2)
实现代码：
class Solution:
ans = []
"""
@param numbers: Give an array numbers of n integer
@return: Find all unique triplets in the array which gives the sum of zero.
"""
def threeSum(self, numbers):
# write your code here
#从大到小排序，想要为0，必须要有正有负
numbers.sort()
right = len(numbers) -1
# b+c = -a, a<=b<=c
for a in range(len(numbers) - 2):
if a > 0 and numbers[a-1] == numbers[a]:
continue
left = a + 1
self.twoSum(numbers, left, right, -numbers[a])
return self.ans
def twoSum(self, numbers, left, right, target):
while left < right:
summation = numbers[left] + numbers[right]
if summation == target:
self.ans.append((-target, numbers[left], numbers[right]))
left, right = left + 1, right - 1
#如果和前一个一样，就重复了
while left < right and numbers[left] == numbers[left - 1]:
left += 1
while left < right and numbers[right] == numbers[right + 1]:
right -= 1
elif summation < target:
left += 1
else:
right -= 1