leetcode: 15. 3Sum

# 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]
# ]

class Solution():
    def threeSum(self, x):
        x.sort()
        res = []
        for left in range(len(x) - 2):
            mid, right = left + 1, len(x) - 1
            while mid < right:
                s = x[left] + x[mid] + x[right]
                if s == 0:
                    if [x[left], x[mid], x[right]] not in res:
                        res.append([x[left], x[mid], x[right]])
                    mid, right = mid + 1, right - 1
                elif s < 0:
                    mid += 1
                else:
                    right -= 1
        return res


if __name__ == '__main__':
    assert Solution().threeSum([-1, 0, 1, 2, -1, -4]) == [[-1, -1, 2], [-1, 0, 1]]
    assert Solution().threeSum([1 ,1, 1, -2]) == [[-2, 1, 1]]

class Solution():
     def threeSum(self, x):
        x.sort()
        res = []
        for left in range(len(x) - 2):
            if left == 0 or x[left] != x[left-1] and x[left] <= 0:
                mid, right = left + 1, len(x) - 1
                while mid < right:
                    s = x[left] + x[mid] + x[right]
                    if s == 0:
                        res.append([x[left], x[mid], x[right]])
                        mid, right = mid + 1, right - 1
                        while mid < right and x[mid] == x[mid - 1]:
                            mid += 1
                        while mid < right and x[right] == x[right + 1]:
                            right -= 1
                    elif s < 0:
                        mid += 1
                    else:
                        right -= 1
        return res


if __name__ == '__main__':
    assert Solution().threeSum([-1, 0, 1, 2, -1, -4]) == [[-1, -1, 2], [-1, 0, 1]]
    assert Solution().threeSum([1 ,1, 1, -2]) == [[-2, 1, 1]]