How to approach the question

#1

how to approach this question

#2

for n elements, a pair is equal to 1 if both the elements in it are strictly one and we need k such pairs, for all the other pairs we need them to be zero i.e. one of the element of those should be zero or both can be zero
considering these constraints you should be able to solve this

#3

hey @souravmunjal2000 if your doubt is sovled, please mark it as resolved