58. 四数之和

class Solution:
    """
    @param numbers: Give an array
    @param target: An integer
    @return: Find all unique quadruplets in the array which gives the sum of zero
    """
    def fourSum(self, numbers, target):
        # write your code here
        #相当于是两个两数之和
        length, res = len(numbers), []
        
        numbers = sorted(numbers)
        
        #固定前面两个值
        for i in range(3, length):
            #如果是相等的话，则跳过处理
            for j in range(2, i):
                total = target - numbers[i] - numbers[j]
                
                #剩下的两个进行求和,满足total
                left, right = 0, j - 1 
                while left < right:
                    sum = numbers[left] + numbers[right]
                    if sum == total:
                        #判断是否已经存在res里面
                        add_res = [numbers[left], numbers[right], numbers[j], numbers[i]]
                        if add_res not in res:
                            res.append(add_res)
                        right -= 1
                        left += 1
                    elif sum > total:
                        right -= 1 
                    elif sum < total:
                        left += 1 
            
        return res