给定一个数组，找到总和等于给定总和的元素对，并返回其索引的总和

Question

Hey guys as you've read in the question i am trying to find the element pairs in an array equal to the given sum and return the sum of their respective indices.

I was able to return the element pairs for the given sum but failed to return the sum of their indices. Here is my code:

arr = [1, 4, 2, 3, 0 , 5]
sum = 7

x = min(arr)
y = max(arr)

while x < y:
    if x + y > sum:
        y -= 1
    elif x + y < sum:
        x += 1
    else:
        print("(", x, y, ")")
        x += 1

My output:

( 2 5 )    
( 3 4 )

This is what i need to do further:

2 + 5 = 7 → Indices 2 + 5 = 7;

3 + 4 = 7 → Indices 3 + 1 = 4;

7 + 4 = 11 → Return 11;

Thanks in Advance!

Answer 1

you can try using a nested loop :

arr = [1, 4, 2, 3, 0 , 5]
sums = 7
tlist = []
for i in range(len(arr)):
    for j in range(len(arr)-1):
        if (i!=j) and ((arr[i] + arr[j+1]) == sums):
            if (i,j+1) not in tlist and (j+1,i) not in tlist:
                tlist.append((i,j+1))
                print("index ->",i,"   ",j+1)
                print("sum=", i+j+1)

output:

index -> 1     3
sum= 4
index -> 2     5
sum= 7

Answer 2

You could use itertools for easily checking sum for combinations like,

>>> import itertools
>>> num = 7
>>> for a,b in itertools.combinations(arr, 2):
...   if a + b == num:
        aindex, bindex = arr.index(a), arr.index(b)
...     indices_sum = aindex + bindex
...     print('[element sum]: {} + {} = {} [indices sum]: {} + {} = {}'.format(a, b, a + b, aindex, bindex , indices_sum))
... 
[element sum]: 4 + 3 = 7 [indices sum]: 1 + 3 = 4
[element sum]: 2 + 5 = 7 [indices sum]: 2 + 5 = 7
>>> arr
[1, 4, 2, 3, 0, 5]

Answer 3

You could take a different approach by calculating the difference then checking if each element is present in the first array or not.

arr = [1, 4, 2, 3, 0, 5]
the_sum = 7

diff = [the_sum - x for x in arr]
for idx, elem in enumerate(diff):
    try:
        index = arr.index(elem)
        sum_of_indices = idx + index
        print("{} + {} = {}".format(idx, index, sum_of_indices))
    except ValueError:
        pass

output

1 + 3 = 4
2 + 5 = 7
3 + 1 = 4
5 + 2 = 7

To remove the duplicates, its always easy to take a frozenset of the indices tuple

a = [(2,1), (1,2), (3,2), (2,3)]
{frozenset(x) for x in a} # {frozenset({2, 3}), frozenset({1, 2})}