python - 如果列表中的数字等于n，则打印出它们的索引

Question

任务:

You are given two parameters, an array and a number. For all the numbers that make n in pairs of two, return the sum of their indices.

input is: arr = [1, 4, 2, 3, 0, 5] and n = 7

output: 11

since the perfect pairs are (4,3) and (2,5) with indices 1 + 3 + 2 + 5 = 11

到目前为止，我已经有了这个，它可以打印出完美的配对

from itertools import combinations


def pairwise(arr, n):    
    for i in combinations(arr, 2): # for index in combinations in arr, 2 elements
        if i[0] + i[1] == n: # if their sum is equal to n
            print(i[0],i[1])

输出:

4,3 2,5

但是，有人有关于如何打印完美对的索引的提示吗？我应该使用 numpy 还是应该更改整个函数？

Answer 1

您可以生成索引组合，而不是生成数组元素的组合。

from itertools import combinations


def pairwise(arr, n):
    s = 0 
    for i in combinations(range(len(arr)), 2): # for index in combinations in arr, 2 elements
        if arr[i[0]] + arr[i[1]] == n: # if their sum is equal to n
            # print(arr[i[0]],arr[i[1]])
            # print(i[0],i[1])
            s += i[0] + i[1]
    # print(s)
    return s