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]]        """