I am not good in Explaining but still I'm trying, Hope you will get it.

Let's consider Arrays A and B and resultant array C (merged array).

The element from the first array will be appended to C until the element of the second array is larger, For example lets take first Testcase

C= {3 1 4 5 2 6}.

If first element belong to the array A then until next greater element of first element should belong to the same array i.e. {3, 1} should belong to the same array,

moving forward the element {4} would belong to any array, {5,2} belong to any array and {6} belong to any array.

Observe that we are partitioning the elements until its next greater element.

Taking another example C={3, 1, 2, 5, 4, 7, 6, 8}

partitions are {3, 1, 2}, {5, 4}, {7,6}, {8}

Now we have to divide these partitions in two arrays without changing the order.

To divide these partitions we have to use knapsack and mark the partitions that can make two arrays of equal size. Also check that these partitions can divide array equally or not.

In the second example, first and fourth partition should belong to the same array and remaining belong to the another array i.e.

A={3,1,2,8}

B={5,4,7,6}

For reference you can see this code https://codeforces.me/contest/1906/submission/236794036