How do I reduce a nested for loop into one loop?

Question

I am required to form pairs of the form (a,b) from the elements present in an array. So I wrote this:
// consider array int a[] is defined with distinct elements

// N is the number of elements in the array

for(i=0;i<N-1;i++) {
for(j=i+1;j<N;j++) {
// some work with a[i] and a[j]
}
}
}

But I really need to reduce this into one loop so that it takes less time to execute. How can I do that?
Complete code:
https://code.sololearn.com/cv9nq13f9RcK/#cpp

Answer 1

You can use i+1 in place of j and then remove the for of j. Not sure if it will take less time to execute though.

Answer 2

What kind of work you will do with a[i] and a[j]?Everything can change depending on that.
There is an article to speed up the loops
https://www.quora.com/How-can-we-speed-up-the-loop-execution-time-of-nested-loops

Answer 3

What kind of work you will do with a[i] and a[j]?Everything can change depending on that.
There is an article to speed up the loops
https://www.quora.com/How-can-we-speed-up-the-loop-execution-time-of-nested-loops