Three_sum

#coding:utf-8
'''
Created on 2017-9-27

@author: 劉帥
'''
"""
Given an array S of n integers, are there elements a, b, c in S
such that a + b + c = 0?
Find all unique triplets in the array which gives the sum of zero.
Note: The solution set must not contain duplicate triplets.
For example, given array S = [-1, 0, 1, 2, -1, -4],
A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]
"""


def three_sum(nums):
    res = []
    nums.sort()
    for i in range(len(nums) - 2):
        if i > 0 and nums[i] == nums[i - 1]:
            continue
        l,r = i + 1,len(nums) - 1
        while l < r:
            s = nums[i] + nums[l] + nums[r]
            if s > 0:
                r -=1
            elif s < 0:
                l += 1
            else:
                res.append([nums[i],nums[l],nums[r]])
                while l < r and nums[l] == nums[l + 1]:
                    l += 1
                while l < r and nums[r] == nums[r - 1]:
                    r -= 1
                l += 1
                r -= 1
    return res

if __name__ == "__main__":
    x = [-1,0,1,2,-1,-4]
    print(three_sum(x))