leetcode 18:4Sum

class Solution(object):
    def fourSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        length = len(nums)
        nums.sort()
        res = []
        for i in range(0,length-2):
            for j in range(i+1,length-1):
                l,r = j+1,length-1
                while(l