How to find out from the array 2.10python satisfies a + b = c + d is the number of two

Subject description:

Given an array, to find out whether there are two pairs of array (a, b), and (C, d), such that a + b = c + d, wherein a, b, c and d are different elements. If there are multiple answers, print any one can be. For example given array [3,4,7,10,20,9,8], you can be found in a number of two (3,8) and (4,7), such that 3 + 4 + 8 = 7.

Ideas:

The easiest way is to quadruple traverse of all possible pairs of determining whether to meet the requirements, if the print out, time complexity of this method is O (n ** 4);
are presented dictionary method: logarithm traversing unit, during traversal, the sum of the present value of the number of dictionaries ( 键为数对的和，值为数对key), when traversing to a key-value pair, and if it already exists in the dictionary, then meet the conditions found value pairs.

Performance Analysis:
time complexity of O (n ** 2), because of the use of the double loop, the actual time of insertion of the dictionary lookup operation complexity is O (1);

Code:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# @Time    : 2020/1/22 19:31
# @Author  : buu
# @Software: PyCharm
# @Blog    ：https://blog.csdn.net/weixin_44321080
class Pair:
    def __init__(self, first, second):
        self.first = first
        self.second = second


def findPairs(arr):
    sumPair = dict()  # 键为数对的和，值为数对
    n = len(arr)
    i = 0
    while i < n:  # 遍历数组中所有可能的数对
        j = i + 1
        while j < n:
            sums = arr[i] + arr[j]
            if sums not in sumPair.keys():  # 若数对的和在字典的键中不存在，在加入
                sumPair[sums] = Pair(arr[i], arr[j])
            else:  # 若数对的和存在字典的键中，则满足要求，打印出来即可
                p = sumPair[sums]
                print('(' + str(p.first) + ',' + str(p.second) \
                      + ')', '(' + str(arr[i]) + ',' + str(arr[j]) + ')')
                return True
            j += 1
        i += 1
    return False


if __name__ == '__main__':
    arr = [3, 4, 7, 10, 20, 9, 8]
    findPairs(arr)

The results:

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