15. 3Sum

class Solution:
    def threeSum(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        res = []
        nums.sort()
        for i in range(0, len(nums)-2):
            # skip the duplicate
            if i > 0 and nums[i-1] == nums[i]:
                continue

            # Get the target value
            temp = 0 - nums[i]

            # Two pointer from start and end
            l = i + 1
            r = len(nums)-1

            while l < r:
                #在这个while Loop里面要用 if ... elif ... else ...
                if nums[l] + nums[r] == temp:
                    # Get the target numbers group
                    res.append([nums[i],nums[l],nums[r]])

                    # skip the duplicate
                    while l < r and nums[l] == nums[l+1]:
                        l = l + 1
                    while l < r and nums[r] == nums[r-1]:
                        r = r - 1
                    # Next pair numbers
                    l = l + 1
                    r = r - 1

                elif nums[l] + nums[r] < temp:
                    l = l + 1
                else:
                    r = r - 1

        return res