Question

Let’s say I have a fixed sized array. I want to fill the array with either 1s or 2s so that all element sums up to X.

Example:

• Required sum = 12
• Array size = 7

Possible combinations:

array( 1, 2, 2, 2, 1, 2, 2 ) // sums to 12

array( 1, 1, 2, 2, 2, 2, 2 ) // sums to 12

Answer 1

• Find the number of 2’s in the array, this number is:

  #2's = X - array_size
  

• Chose random arbitrary #2's elements (for example the first elements), and
  give them the value 2, the rest of the elements will get the value 1.

Note: it is easy to see that if X < array_size or X> 2*array_size there is no solution to the problem (and obviously the above algorithm will fail)