How i calculate max selects of data from 2 arrays before reach cap

Question

i have 2 arrays (stacks): 9 index is top of stack

[5,1,1,-,-,-] [5,6,5,1,1,1]

I can get only 0 index from arrays and remove it from array How calculate max selects before sum of elements reach <=20? Arrays can be very large

Answer For example: max is 6 (5+6+5+1+1+1) - full sum of 2 array

1. get 5 from 2 array (5 =5)
2. get 6 from 2 array(5+6 =11)
3. get 5 from 2 array(5+6+5 =16)
4. get 1 from 2 array(5+6+5 +1 =17)
5. get 1 from 2 array(5+6+5 +1+1 =18)
6. get 1 from 2 array(5+6+5 +1+1+1 =19)
7. get 5 from 1 array(5+6+5 +1+1+1 +5 =24) we don get this try because 24>20

Other variants (5):

1. get 5 from 1 array (5 =5)
2. get 1 from 1 array(5+1 =6)
3. get 1 from 1 array(5+1+1 =7)
4. get 5 from 2 array(5+1+1 +5 =12)
5. get 6 from 2 array(5+1+1 +5+6 =18) 6.get 5 from 2 array(5+1+1 +5+6+5 =23)we don get this try because 23>20

Answer 1

1. Create a cumulative sum array for both arrays. For example, the cumulative sum for [5,1,1,-,-,-] would be [5,6,7,-,-,-] , and for [5,6,5,1,1,1] it would be [5,11,16,17,18,19] .
2. Use the two pointer approach to find the sum which is closest to the target sum (which is 20 in your case)

If the arrays are guaranteed to have non-negative elements, this approach would have an O(1) complexity.