CODEWITHSUNDEEP
pythonarrayspython-3.xsum
lxarmx
lxarmx

Reputation: 1

Sum of array diagonal

I'm very new at this and have to do this for a project so keep that in mind.

I need to write a function sumOfDiagonal that has one parameter of type list.

The list is a 4x4 2-dimensional array of integers (4 rows and 4 columns of integers).

The function must return the sum of the integers in the diagonal positions from top right to bottom left.

I have not tried anything because I have no idea where to begin, so would appreciate some guidance.

Upvotes: 0

Views: 2139

Answers (1)

paxdiablo
paxdiablo

Reputation: 881293

Since you haven't specified a language (and this is probably classwork anyway), I'll have to provide pseudo-code. Given the 4x4 2d array, the basic idea is to use a loop specifying the index, and use that index to get the correct elements in both dimensions. Say we had the array:

           [][0]  [][1]  [][2]  [][3]
           -----  -----  -----  -----
[0][]          1      2      3      4
[1][]          5      6      7      8
[2][]          9     10     11     12
[3][]         13     14     15     16

and we wanted to sum the top-left-to-bottom-right diagonal (1+6+11+16)(1). That would be something like:

def sumOfDiagonal (arr, sz):
    sum = 0
    for i = 0 to sz - 1 inclusive:
        sum = sum + arr[i][i]
    return sum

That's using the normal means of accessing an array. If, as may be given the ambiguity in the question, your array is actually a list of some description (such as a linked list of sixteen elements), you'll just need to adjust how you get the "array" elements.

For example, a 16-element list would need to get nodes 0, 5, 10 and 15 so you could run through the list skipping four nodes after each accumulation.

By way of example, here's some Python code(2) for doing the top-left-to-bottom-right variant, which outputs 34 (1+6+11+16) as expected:

def sumOfDiagonals(arr):
    sum = 0
    for i in range(len(arr)):
        sum += arr[i][i]
    return sum

print(sumOfDiagonals([[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]]))

(1) To do top right to bottom left simply requires you to change the second term into sz - i - 1.

(2) Python is the ideal pseudo-code language when you want to be able to test your pseudo-code, provided you stay away from its more complex corners :-)

Upvotes: 2

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