15. 3Sum【M】【28】

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:

• Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
• 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)

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关键在于两个指针，如果和小于零，左边的坐标增长，反之右边的左边增长

class Solution(object):
    def threeSum(self, nums):

        nums.sort()
        #print nums
        res = []
        minn = 1 << 31

        for i in xrange(len(nums)):
            a = 0
            b = len(nums) - 1
            while a < i and b > i:
                print i,a,b,nums[a],nums[i],nums[b]
                if nums[a] + nums[b] + nums[i] == 0:
                    if [nums[a],nums[i],nums[b]] not in res:
                        res += [nums[a],nums[i],nums[b]],
                    a += 1
                    b -= 1
                    continue
                if nums[a] + nums[b] + nums[i] <= 0:
                    a += 1
                else:
                    b -= 1

        '''
        #nums = set(nums)
        #print nums
        minn = 1 << 31
        #print minn
        res = []

        per = itertools.combinations(nums,3)
        for i in per:
            #print i
            summ = sum(i)#i[0] + i[1] + i[2]
            if summ == 0 and i not in res:
                res.append(i)

        #for i in xrange(len(nums)):
        #    print nums[i]
        '''
        return res

        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """